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621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
circumstances among amphibians is wide, with many discoveries still being made.
## Eggs.
The egg of an amphibian is typically surrounded by a transparent gelatinous covering secreted by the oviducts and containing mucoproteins and mucopolysaccharides. This capsule is permeable to water and gases, and swells... | 28,000 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
oxygen to the embryo through photosynthesis. They seem to both speed up the development of the larvae and reduce mortality. Most eggs contain the pigment melanin which raises their temperature through the absorption of light and also protects them against ultraviolet radiation. Caecilians, some plethodontid s... | 28,001 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
caecilians, the eggs are laid in grape-like clusters in burrows near streams. The amphibious salamander "Ensatina" attaches its similar clusters by stalks to underwater stems and roots. The greenhouse frog ("Eleutherodactylus planirostris") lays eggs in small groups in the soil where they develop in about two... | 28,002 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
by the female.
## Larvae.
The eggs of amphibians are typically laid in water and hatch into free-living larvae that complete their development in water and later transform into either aquatic or terrestrial adults. In many species of frog and in most lungless salamanders (Plethodontidae), direct development... | 28,003 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
secretions and develop within the female's oviduct, often for long periods. Other amphibians, but not caecilians, are ovoviviparous. The eggs are retained in or on the parent's body, but the larvae subsist on the yolks of their eggs and receive no nourishment from the adult. The larvae emerge at varying stage... | 28,004 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
some species (such as "Nannophrys ceylonensis") are semi-terrestrial and live among wet rocks. Tadpoles have cartilaginous skeletons, gills for respiration (external gills at first, internal gills later), lateral line systems and large tails that they use for swimming. Newly hatched tadpoles soon develop gill... | 28,005 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
teeth, in most species, the jaws have long, parallel rows of small keratinized structures called keradonts surrounded by a horny beak. Front legs are formed under the gill sac and hind legs become visible a few days later.
Iodine and T4 (over stimulate the spectacular apoptosis [programmed cell death] of the... | 28,006 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
fins and small mouths; they swim in the quiet waters feeding on growing or loose fragments of vegetation. Stream dwellers mostly have larger mouths, shallow bodies and caudal fins; they attach themselves to plants and stones and feed on the surface films of algae and bacteria. They also feed on diatoms, filte... | 28,007 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
younger tadpoles attacking a larger, more developed tadpole when it is undergoing metamorphosis.
At metamorphosis, rapid changes in the body take place as the lifestyle of the frog changes completely. The spiral‐shaped mouth with horny tooth ridges is reabsorbed together with the spiral gut. The animal devel... | 28,008 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
take place.
### Salamanders.
At hatching, a typical salamander larva has eyes without lids, teeth in both upper and lower jaws, three pairs of feathery external gills, a somewhat laterally flattened body and a long tail with dorsal and ventral fins. The forelimbs may be partially developed and the hind limb... | 28,009 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
but this varies with species and with populations. The northwestern salamander ("Ambystoma gracile") is one of these and, depending on environmental factors, either remains permanently in the larval state, a condition known as neoteny, or transforms into an adult. Both of these are able to breed. Neoteny occu... | 28,010 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
way and may grow particularly large in the process. The adult tiger salamander is terrestrial, but the larva is aquatic and able to breed while still in the larval state. When conditions are particularly inhospitable on land, larval breeding may allow continuation of a population that would otherwise die out.... | 28,011 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
a large yolk sac and the larva feeds on this while it develops inside the egg, emerging fully formed as a juvenile salamander. The female salamander often broods the eggs. In the genus "Ensatinas", the female has been observed to coil around them and press her throat area against them, effectively massaging t... | 28,012 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
gill sacs and are reabsorbed just before the animals leave the water. Other changes include the reduction in size or loss of tail fins, the closure of gill slits, thickening of the skin, the development of eyelids, and certain changes in dentition and tongue structure. Salamanders are at their most vulnerable... | 28,013 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
absorbed upon leaving the water for the first time.
### Caecilians.
Most terrestrial caecilians that lay eggs do so in burrows or moist places on land near bodies of water. The development of the young of "Ichthyophis glutinosus", a species from Sri Lanka, has been much studied. The eel-like larvae hatch ou... | 28,014 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
developed a pointed head with sensory tentacles near the mouth and lost their eyes, lateral line systems and tails. The skin thickens, embedded scales develop and the body divides into segments. By this time, the caecilian has constructed a burrow and is living on land.
In the majority of species of caecilia... | 28,015 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
the ciliated epithelial cells that line the oviduct. This stimulates the secretion of fluids rich in lipids and mucoproteins on which they feed along with scrapings from the oviduct wall. They may increase their length sixfold and be two-fifths as long as their mother before being born. By this time they have... | 28,016 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
as maternal dermatophagy. The brood feed as a batch for about seven minutes at intervals of approximately three days which gives the skin an opportunity to regenerate. Meanwhile, they have been observed to ingest fluid exuded from the maternal cloaca.
## Parental care.
The care of offspring among amphibians... | 28,017 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
of behaviour in the care of their young.
Many woodland salamanders lay clutches of eggs under dead logs or stones on land. The black mountain salamander ("Desmognathus welteri") does this, the mother brooding the eggs and guarding them from predation as the embryos feed on the yolks of their eggs. When fully... | 28,018 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
a tiny frog, protects the egg cluster which is hidden under a stone or log. When the eggs hatch, the male transports the tadpoles on his back, stuck there by a mucous secretion, to a temporary pool where he dips himself into the water and the tadpoles drop off. The male midwife toad ("Alytes obstetricans") wi... | 28,019 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
The tadpoles secrete a hormone that inhibits digestion in the mother whilst they develop by consuming their very large yolk supply. The pouched frog ("Assa darlingtoni") lays eggs on the ground. When they hatch, the male carries the tadpoles around in brood pouches on his hind legs. The aquatic Surinam toad (... | 28,020 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
of a leaf or the rosette of a bromeliad. The female visits the nursery sites regularly and deposits unfertilised eggs in the water and these are consumed by the tadpoles.
# Feeding and diet.
With a few exceptions, adult amphibians are predators, feeding on virtually anything that moves that they can swallow... | 28,021 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
adapted tongue for picking up ants and termites. It projects it with the tip foremost whereas other frogs flick out the rear part first, their tongues being hinged at the front.
Food is mostly selected by sight, even in conditions of dim light. Movement of the prey triggers a feeding response. Frogs have bee... | 28,022 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
normally hunt by smell. Some salamanders seem to have learned to recognize immobile prey when it has no smell, even in complete darkness.
Amphibians usually swallow food whole but may chew it lightly first to subdue it. They typically have small hinged pedicellate teeth, a feature unique to amphibians. The b... | 28,023 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
mouth.
The tiger salamander ("Ambystoma tigrinum") is typical of the frogs and salamanders that hide under cover ready to ambush unwary invertebrates. Others amphibians, such as the "Bufo spp." toads, actively search for prey, while the Argentine horned frog ("Ceratophrys ornata") lures inquisitive prey clos... | 28,024 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
The struggles of the prey and further jaw movements work it inwards and the caecilian usually retreats into its burrow. The subdued prey is gulped down whole.
When they are newly hatched, frog larvae feed on the yolk of the egg. When this is exhausted some move on to feed on bacteria, algal crusts, detritus ... | 28,025 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
many kinds as well as stirring up the bottom sediment, filtering out larger particles with the papillae around their mouths. Some, such as the spadefoot toads, have strong biting jaws and are carnivorous or even cannibalistic.
# Vocalization.
The calls made by caecilians and salamanders are limited to occas... | 28,026 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
squeak or yelp if attacked.
Frogs are much more vocal, especially during the breeding season when they use their voices to attract mates. The presence of a particular species in an area may be more easily discerned by its characteristic call than by a fleeting glimpse of the animal itself. In most species, t... | 28,027 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
a female to approach and discourage other males from intruding on its territory. This call is modified to a quieter courtship call on the approach of a female or to a more aggressive version if a male intruder draws near. Calling carries the risk of attracting predators and involves the expenditure of much en... | 28,028 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
hours.
# Territorial behaviour.
Little is known of the territorial behaviour of caecilians, but some frogs and salamanders defend home ranges. These are usually feeding, breeding or sheltering sites. Males normally exhibit such behaviour though in some species, females and even juveniles are also involved. ... | 28,029 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
This may involve snapping, chasing and sometimes biting, occasionally causing the loss of a tail. The behaviour of red back salamanders ("Plethodon cinereus") has been much studied. 91% of marked individuals that were later recaptured were within a metre (yard) of their original daytime retreat under a log or... | 28,030 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
did not involve any actual contact between individuals. An aggressive posture involved raising the body off the ground and glaring at the opponent who often turned away submissively. If the intruder persisted, a biting lunge was usually launched at either the tail region or the naso-labial grooves. Damage to ... | 28,031 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
a heavier and more powerful individual, and this may be sufficient to prevent intrusion by smaller males. Much energy is used in the vocalization and it takes a toll on the territory holder who may be displaced by a fitter rival if he tires. There is a tendency for males to tolerate the holders of neighbourin... | 28,032 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
splashing, and ducking him under the water.
# Defence mechanisms.
Amphibians have soft bodies with thin skins, and lack claws, defensive armour, or spines. Nevertheless, they have evolved various defence mechanisms to keep themselves alive. The first line of defence in salamanders and frogs is the mucous se... | 28,033 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
("Typhlonectes compressicauda") produces toxic mucus that has killed predatory fish in a feeding experiment in Brazil. In some salamanders, the skin is poisonous. The rough-skinned newt ("Taricha granulosa") from North America and other members of its genus contain the neurotoxin tetrodotoxin (TTX), the most ... | 28,034 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
("Thamnophis sirtalis").
In locations where both snake and salamander co-exist, the snakes have developed immunity through genetic changes and they feed on the amphibians with impunity. Coevolution occurs with the newt increasing its toxic capabilities at the same rate as the snake further develops its immun... | 28,035 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
species often use bright colouring to warn potential predators of their toxicity. These warning colours tend to be red or yellow combined with black, with the fire salamander ("Salamandra salamandra") being an example. Once a predator has sampled one of these, it is likely to remember the colouration next tim... | 28,036 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
amphibians are nocturnal and hide during the day, thereby avoiding diurnal predators that hunt by sight. Other amphibians use camouflage to avoid being detected. They have various colourings such as mottled browns, greys and olives to blend into the background. Some salamanders adopt defensive poses when face... | 28,037 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
The tail may have a constriction at its base to allow it to be easily detached. The tail is regenerated later, but the energy cost to the animal of replacing it is significant.
Some frogs and toads inflate themselves to make themselves look large and fierce, and some spadefoot toads ("Pelobates spp") scream ... | 28,038 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
Cognition.
In amphibians, there is evidence of habituation, associative learning through both classical and instrumental learning, and discrimination abilities.
In one experiment, when offered live fruit flies ("Drosophila virilis"), salamanders chose the larger of 1 vs 2 and 2 vs 3. Frogs can distinguish b... | 28,039 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
extinction, have been noted since the late 1980s from locations all over the world, and amphibian declines are thus perceived to be one of the most critical threats to global biodiversity. In 2004, the International Union for Conservation of Nature (IUCN) reported stating that currently birds, mammals, and am... | 28,040 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
there was insufficient data to assess their status. A number of causes are believed to be involved, including habitat destruction and modification, over-exploitation, pollution, introduced species, climate change, endocrine-disrupting pollutants, destruction of the ozone layer (ultraviolet radiation has shown... | 28,041 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
one of the largest parts of the vertebrate biomass. Any decline in amphibian numbers will affect the patterns of predation. The loss of carnivorous species near the top of the food chain will upset the delicate ecosystem balance and may cause dramatic increases in opportunistic species. In the Middle East, a ... | 28,042 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
and the mountain yellow-legged frog ("Rana muscosa"), putting the snake's future at risk. If the snake were to become scarce, this would affect birds of prey and other predators that feed on it. Meanwhile, in the ponds and lakes, fewer frogs means fewer tadpoles. These normally play an important role in contr... | 28,043 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
the crisis was released in 2005 in the form of the Amphibian Conservation Action Plan. Developed by over eighty leading experts in the field, this call to action details what would be required to curtail amphibian declines and extinctions over the following five years and how much this would cost. The Amphibi... | 28,044 |
621 | Amphibian | https://en.wikipedia.org/w/index.php?title=Amphibian | Amphibian
ld, encouraging them to create assurance colonies of threatened amphibians. One such project is the Panama Amphibian Rescue and Conservation Project that built on existing conservation efforts in Panama to create a country-wide response to the threat of chytridiomycosis.
# See also.
- List of amphibians
- ... | 28,045 |
206718 | Summer and Smoke | https://en.wikipedia.org/w/index.php?title=Summer%20and%20Smoke | Summer and Smoke
Summer and Smoke
Summer and Smoke is a two-part, thirteen-scene 1948 play by Tennessee Williams, originally titled "Chart of Anatomy" when Williams began work on it in 1945. The phrase "summer and smoke" probably comes from the Hart Crane poem "Emblems of Conduct" in the 1926 collection "White Buildin... | 28,046 |
206718 | Summer and Smoke | https://en.wikipedia.org/w/index.php?title=Summer%20and%20Smoke | Summer and Smoke
nearly blossoms between her and John Buchanan Jr., a wild, undisciplined young doctor who grew up next door. She, ineffably refined, identifies with the Gothic cathedral, "reaching up to something beyond attainment"; her name, as Williams makes clear during the play, means "soul" in Spanish; whereas Bu... | 28,047 |
206718 | Summer and Smoke | https://en.wikipedia.org/w/index.php?title=Summer%20and%20Smoke | Summer and Smoke
But he has changed, he is engaged to settle down with a respectable, younger girl; and, as he tries to convince Alma that what they had between them was indeed a "spiritual bond", she realizes, in any event, that it is too late. In the final scene, Alma accosts a young traveling salesman at dusk in the... | 28,048 |
206718 | Summer and Smoke | https://en.wikipedia.org/w/index.php?title=Summer%20and%20Smoke | Summer and Smoke
by Margo Jones and designed by Jo Mielziner with Tod Andrews, Margaret Phillips, Monica Boyar and Anne Jackson. The play ran for 102 performances, and at the time, represented a downturn in popularity for Williams following his successful "A Streetcar Named Desire".
In 1952, Geraldine Page played the ... | 28,049 |
206718 | Summer and Smoke | https://en.wikipedia.org/w/index.php?title=Summer%20and%20Smoke | Summer and Smoke
play on the radio series "Best Plays" in 1953 opposite Richard Kiley (recordings of which still exist). She also portrayed Alma Winemiller in the 1961 film version opposite Laurence Harvey, earning an Academy Award nomination (as did Una Merkel playing her mother). Additional Oscar nominations went to ... | 28,050 |
206718 | Summer and Smoke | https://en.wikipedia.org/w/index.php?title=Summer%20and%20Smoke | Summer and Smoke
The production stage manager was Henry Banister and press was by Seymour Krawitz, Patricia McLean Krawitz and Louise Ment. The show starred Betsy Palmer (Alma), Shepperd Strudwick (Rev. Winemiller), Grace Carney (Mrs. Winemiller), Nan Martin (Mrs. Buchanan), Peter Blaxill (Roger Doremus), Jen Jones (Mr... | 28,051 |
206718 | Summer and Smoke | https://en.wikipedia.org/w/index.php?title=Summer%20and%20Smoke | Summer and Smoke
been notable Almas in regional productions.
It was nearly 60 years before the London premiere of "Summer and Smoke". It opened at the Apollo Theatre on 17 October 2006. The production, directed by Adrian Noble and starring Rosamund Pike and Chris Carmack, first opened at the Nottingham Playhouse in Se... | 28,052 |
206718 | Summer and Smoke | https://en.wikipedia.org/w/index.php?title=Summer%20and%20Smoke | Summer and Smoke
the play, titled "The Eccentricities of a Nightingale", which received a favorable notice from "The New York Times".
In 2017, the Almeida Theatre announced a new production starring Patsy Ferran, directed by Rebecca Frecknall and designed by Tom Scutt. After a successful run and several five-star revi... | 28,053 |
206718 | Summer and Smoke | https://en.wikipedia.org/w/index.php?title=Summer%20and%20Smoke | Summer and Smoke
cted by Peter Glenville, and starred Laurence Harvey, Rita Moreno, and Geraldine Page reprising her role as Alma. A television version was produced in 1972, starring Lee Remick, David Hedison, and Barry Morse. Another production, titled "Eccentricities of a Nightingale", starring Blythe Danner and Fran... | 28,054 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
Alkane
In organic chemistry, an alkane, or paraffin (a historical name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carbon–carbon bonds are single. Alkanes have the general chemic... | 28,055 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
therefore consisting entirely of hydrogen atoms and saturated carbon atoms". However, some sources use the term to denote "any" saturated hydrocarbon, including those that are either monocyclic (i.e. the cycloalkanes) or polycyclic, despite their having a different general formula (i.e. cycloalkanes are CH).
In... | 28,056 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
solids at standard ambient temperature and pressure (SATP), for which the number of carbon atoms in the carbon backbone is greater than about 17.
With their repeated –CH units, the alkanes constitute a homologous series of organic compounds in which the members differ in molecular mass by multiples of 14.03 u (... | 28,057 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
petroleum (crude oil) and natural gas.
An alkyl group, generally abbreviated with the symbol R, is a functional group that, like an alkane, consists solely of single-bonded carbon and hydrogen atoms connected acyclically—for example, a methyl or ethyl group.
# Structure and classification.
Saturated hydrocarb... | 28,058 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
to the definition by IUPAC, the former two are alkanes, whereas the third group is called cycloalkanes. Saturated hydrocarbons can also combine any of the linear, cyclic (e.g., polycyclic) and branching structures; the general formula is , where "k" is the number of independent loops. Alkanes are the acyclic (lo... | 28,059 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
most common). However the chain of carbon atoms may also be branched at one or more points. The number of possible isomers increases rapidly with the number of carbon atoms. For example, for acyclic alkanes:
- C: methane only
- C: ethane only
- C: propane only
- C: 2 isomers: "n"-butane and isobutane
- C: 3... | 28,060 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
center at carbon atom number 3. In addition to the alkane isomers, the chain of carbon atoms may form one or more loops. Such compounds are called cycloalkanes. Stereoisomers and cyclic compounds are excluded when calculating the number of isomers above.
# Nomenclature.
The IUPAC nomenclature (systematic way o... | 28,061 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
(or -yne), -one, -une, for the hydrocarbons CH, CH, CH, CH, CH. Now, the first three name hydrocarbons with single, double and triple bonds; "-one" represents a ketone; "-ol" represents an alcohol or OH group; "-oxy-" means an ether and refers to oxygen between two carbons, so that methoxymethane is the IUPAC na... | 28,062 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
only one side-group. Symmetric compounds will have two ways of arriving at the same name.
## Linear alkanes.
Straight-chain alkanes are sometimes indicated by the prefix ""n"-" (for "normal") where a non-linear isomer exists. Although this is not strictly necessary, the usage is still common in cases where the... | 28,063 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
propane: CH – three carbon and 8 hydrogen
- butane : CH – four carbon and 10 hydrogen
- pentane: CH – five carbon and 12 hydrogen
- hexane : CH – six carbon and 14 hydrogen
The first four names were derived from methanol, ether, propionic acid and butyric acid, respectively (hexadecane is also sometimes refe... | 28,064 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
use the Latin prefix non-. For a more complete list, see List of alkanes.
## Branched alkanes.
Simple branched alkanes often have a common name using a prefix to distinguish them from linear alkanes, for example "n"-pentane, isopentane, and neopentane.
IUPAC naming conventions can be used to produce a systema... | 28,065 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
for the side-chains
- Number and name the side chains before the name of the root chain
- If there are multiple side chains of the same type, use prefixes such as "di-" and "tri-" to indicate it as such, and number each one.
- Add side chain names in alphabetical (disregarding "di-" etc. prefixes) order in fr... | 28,066 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
with respect to the number of carbon atoms in their backbones, e.g., cyclopentane (CH) is a cycloalkane with 5 carbon atoms just like pentane (CH), but they are joined up in a five-membered ring. In a similar manner, propane and cyclopropane, butane and cyclobutane, etc.
Substituted cycloalkanes are named simil... | 28,067 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
artifacts. They were coined before the development of systematic names, and have been retained due to familiar usage in industry. Cycloalkanes are also called naphthenes.
It is almost certain that the term 'paraffin' stems from the petrochemical industry. Branched-chain alkanes are called isoparaffins. The use ... | 28,068 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
properties.
All alkanes are colorless. Alkanes with the lowest molecular weights are gasses, those of intermediate molecular weight are liquids, and the heaviest are waxy solids.
## Boiling point.
Alkanes experience intermolecular van der Waals forces. Stronger intermolecular van der Waals forces give rise to... | 28,069 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
point of alkanes is primarily determined by weight, it should not be a surprise that the boiling point has almost a linear relationship with the size (molecular weight) of the molecule. As a rule of thumb, the boiling point rises 20–30 °C for each carbon added to the chain; this rule applies to other homologous ... | 28,070 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
For the latter case, two molecules 2,3-dimethylbutane can "lock" into each other better than the cross-shaped 2,2-dimethylbutane, hence the greater van der Waals forces.
On the other hand, cycloalkanes tend to have higher boiling points than their linear counterparts due to the locked conformations of the molec... | 28,071 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
fixed structure than liquids. This rigid structure requires energy to break down. Thus the better put together solid structures will require more energy to break apart. For alkanes, this can be seen from the graph above (i.e., the blue line). The odd-numbered alkanes have a lower trend in melting points than eve... | 28,072 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
the corresponding straight-chain alkanes, again depending on the ability of the alkane in question to pack well in the solid phase: This is particularly true for isoalkanes (2-methyl isomers), which often have melting points higher than those of the linear analogues.
## Conductivity and solubility.
Alkanes do ... | 28,073 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
in entropy). As there is no significant bonding between water molecules and alkane molecules, the second law of thermodynamics suggests that this reduction in entropy should be minimized by minimizing the contact between alkane and water: Alkanes are said to be hydrophobic in that they repel water.
Their solubi... | 28,074 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
structure of the alkanes directly affects their physical and chemical characteristics. It is derived from the electron configuration of carbon, which has four valence electrons. The carbon atoms in alkanes are always sp-hybridized, that is to say that the valence electrons are said to be in four equivalent orbit... | 28,075 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
of a hydrogen; the latter by the overlap of two sp orbitals on different carbon atoms. The bond lengths amount to 1.09 × 10 m for a C–H bond and 1.54 × 10 m for a C–C bond.
The spatial arrangement of the bonds is similar to that of the four sp orbitals—they are tetrahedrally arranged, with an angle of 109.47° b... | 28,076 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
between the atoms or groups bound to the atoms at each end of the bond. The spatial arrangement described by the torsion angles of the molecule is known as its conformation.
Ethane forms the simplest case for studying the conformation of alkanes, as there is only one C–C bond. If one looks down the axis of the ... | 28,077 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
between 0° and 360°. This is a consequence of the free rotation about a carbon–carbon single bond. Despite this apparent freedom, only two limiting conformations are important: eclipsed conformation and staggered conformation.
The two conformations, also known as rotamers, differ in energy: The staggered confor... | 28,078 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
to the next, equivalent to the rotation of one CH group by 120° relative to the other, is of the order of 10 seconds.
The case of higher alkanes is more complex but based on similar principles, with the antiperiplanar conformation always being the most favored around each carbon–carbon bond. For this reason, al... | 28,079 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
all organic compounds contain carbon–carbon, and carbon–hydrogen bonds, and so show some of the features of alkanes in their spectra. Alkanes are notable for having no other groups, and therefore for the "absence" of other characteristic spectroscopic features of a different functional group like –OH, –CHO, –COO... | 28,080 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
with more than four carbon atoms show a weak absorption at around 725 cm.
### NMR spectroscopy.
The proton resonances of alkanes are usually found at "δ" = 0.5–1.5. The carbon-13 resonances depend on the number of hydrogen atoms attached to the carbon: "δ" = 8–30 (primary, methyl, –CH), 15–55 (secondary, methy... | 28,081 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
ion is usually weak. The fragmentation pattern can be difficult to interpret, but, in the case of branched chain alkanes, the carbon chain is preferentially cleaved at tertiary or quaternary carbons due to the relative stability of the resulting free radicals. The fragment resulting from the loss of a single met... | 28,082 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
acids). This inertness is the source of the term "paraffins" (with the meaning here of "lacking affinity"). In crude oil the alkane molecules have remained chemically unchanged for millions of years.
However redox reactions of alkanes, in particular with oxygen and the halogens, are possible as the carbon atoms... | 28,083 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
In addition, alkanes have been shown to interact with, and bind to, certain transition metal complexes in C–H bond activation.
Free radicals, molecules with unpaired electrons, play a large role in most reactions of alkanes, such as cracking and reformation where long-chain alkanes are converted into shorter-ch... | 28,084 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
alkanes react with oxygen in a combustion reaction, although they become increasingly difficult to ignite as the number of carbon atoms increases. The general equation for complete combustion is:
In the absence of sufficient oxygen, carbon monoxide or even soot can be formed, as shown below:
For example, metha... | 28,085 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
in a so-called "free radical halogenation" reaction. The hydrogen atoms of the alkane are progressively replaced by halogen atoms. Free radicals are the reactive species that participate in the reaction, which usually leads to a mixture of products. The reaction is highly exothermic, and can lead to an explosion... | 28,086 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
where the radicals recombine.
Experiments have shown that all halogenation produces a mixture of all possible isomers, indicating that all hydrogen atoms are susceptible to reaction. The mixture produced, however, is not a statistical mixture: Secondary and tertiary hydrogen atoms are preferentially replaced du... | 28,087 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
of acid catalysts (usually solid acids such as silica-alumina and zeolites), which promote a heterolytic (asymmetric) breakage of bonds yielding pairs of ions of opposite charges, usually a carbocation and the very unstable hydride anion. Carbon-localized free radicals and cations are both highly unstable and un... | 28,088 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
or ion recombination.
## Isomerization and reformation.
Dragan and his colleague were the first to report about isomerization in alkanes. Isomerization and reformation are processes in which straight-chain alkanes are heated in the presence of a platinum catalyst. In isomerization, the alkanes become branched-... | 28,089 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
alkanes with high octane numbers.
## Other reactions.
Alkanes will react with steam in the presence of a nickel catalyst to give hydrogen. Alkanes can be chlorosulfonated and nitrated, although both reactions require special conditions. The fermentation of alkanes to carboxylic acids is of some technical impor... | 28,090 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
gas planets such as Jupiter (0.1% methane, 2 ppm ethane), Saturn (0.2% methane, 5 ppm ethane), Uranus (1.99% methane, 2.5 ppm ethane) and Neptune (1.5% methane, 1.5 ppm ethane). Titan (1.6% methane), a satellite of Saturn, was examined by the "Huygens" probe, which indicated that Titan's atmosphere periodically ... | 28,091 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
away from the Sun, which would have evaporated these volatile molecules. Alkanes have also been detected in meteorites such as carbonaceous chondrites.
## Occurrence of alkanes on Earth.
Traces of methane gas (about 0.0002% or 1745 ppb) occur in the Earth's atmosphere, produced primarily by methanogenic microo... | 28,092 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
of ancient seas and were covered with sediments in an anoxic environment and converted over many millions of years at high temperatures and high pressure to their current form. Natural gas resulted thereby for example from the following reaction:
These hydrocarbon deposits, collected in porous rocks trapped ben... | 28,093 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
have a low solubility in water, so the content in the oceans is negligible; however, at high pressures and low temperatures (such as at the bottom of the oceans), methane can co-crystallize with water to form a solid methane clathrate (methane hydrate). Although this cannot be commercially exploited at the prese... | 28,094 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
alkanes: they prefer even-numbered carbon chains as they are easier to degrade than odd-numbered chains.
On the other hand, certain archaea, the methanogens, produce large quantities of methane by the metabolism of carbon dioxide or other oxidized organic compounds. The energy is released by the oxidation of hy... | 28,095 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
in the intestines of humans. Methanogenic archaea are, hence, at the end of the carbon cycle, with carbon being released back into the atmosphere after having been fixed by photosynthesis. It is probable that our current deposits of natural gas were formed in a similar way.
- Fungi and plants
Alkanes also play... | 28,096 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
regions.
In plants, the solid long-chain alkanes are found in the plant cuticle and epicuticular wax of many species, but are only rarely major constituents. They protect the plant against water loss, prevent the leaching of important minerals by the rain, and protect against bacteria, fungi, and harmful insect... | 28,097 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
alkanes are also produced by and found in plant tissues. The Jeffrey pine is noted for producing exceptionally high levels of "n"-heptane in its resin, for which reason its distillate was designated as the zero point for one octane rating. Floral scents have also long been known to contain volatile alkane compon... | 28,098 |
639 | Alkane | https://en.wikipedia.org/w/index.php?title=Alkane | Alkane
spectrum of carbon numbers, mainly 8 to 35, usually peaking in the low to upper 20s, with concentrations up to dozens of milligrams per kilogram (parts per million by weight) and sometimes over a hundred for the total alkane fraction.
- Animals
Alkanes are found in animal products, although they are less impor... | 28,099 |
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