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91.49706268310547 183 WikiText2 |
650 = = Modifications = = |
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651 Mint records indicate the first gold dollars were produced on May 7 , 1849 ; Longacre 's diary notes state instead that the first were struck on May 8 . A few coins in proof condition were struck on the first day , along with about 1 @,@ 000 for circulation . There are five major varieties of the 1849 gold dollar ... |
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652 The continued flow of gold from California made silver expensive in terms of gold , and U.S. silver coins began to flow out of the country for melting in 1849 , a flow that accelerated over the next several years as the price of the metal continued to rise . By 1853 , a thousand dollars in silver coin contained $ ... |
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653 As early as 1851 , New York Congressman William Duer alleged that that Patterson had made the gold dollar too small in diameter on purpose to provoke criticism . Patterson retired that year after 16 years in his position , and under his successor , George N. Eckert , annular gold dollar and half dollar patterns we... |
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654 The Act of February 21 , 1853 , that had lightened the silver coins also authorized a gold three @-@ dollar piece , which began to be produced in 1854 . To ensure that the three @-@ dollar piece was not mistaken for other gold coins , it had been made thinner and wider than it would normally be , and Longacre put ... |
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655 Nevertheless , the Type 2 gold dollar ( as it came to be known ) proved unsatisfactory as the mints had difficulty in striking the new coin so that all details were brought out . This was due to the high relief of the design — the three Southern branch mints especially had trouble with the piece . Many of the Type... |
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656 = = = Design of Type 2 and 3 dollars = = = |
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657 The Type 2 and 3 gold dollars depict Liberty as a Native American princess , with a fanciful feathered headdress not resembling any worn by any Indian tribe . This image is an inexact copy of the design Longacre had made for the three @-@ dollar piece , and is one of a number of versions of Liberty Longacre create... |
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658 Art historian Cornelius Vermeule deprecated the Indian princess design used by Longacre for the obverses of the Types 2 and 3 gold dollar , and for the three @-@ dollar piece , " the ' princess ' of the gold coins is a banknote engraver 's elegant version of folk art of the 1850s . The plumes or feathers are more ... |
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659 = = War years = = |
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660 The gold dollar continued to be produced in the late 1850s , though mintages declined from the figures of two million or more each year between 1850 and 1854 . Only about 51 @,@ 000 gold dollars were produced in 1860 , with over two @-@ thirds of that figure at Philadelphia , just under a third at San Francisco , ... |
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661 The other candidate for the rarest from that mint is the 1861 @-@ D , with an estimated mintage of 1 @,@ 000 and perhaps 45 to 60 known . Two pairs of dies were shipped from Philadelphia to Dahlonega on December 10 , 1860 ; they arrived on January 7 , 1861 , two weeks before Georgia voted to secede from the Union ... |
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662 Dahlonega , like the other two branch mints in the South , closed its doors after the 1861 strikings . It and the Charlotte facility never reopened ; the New Orleans Mint again struck coins from 1879 to 1909 , but did not strike gold dollars again . After 1861 , the only issuance of gold dollars outside Philadelph... |
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663 The outbreak of the Civil War shook public confidence in the Union , and citizens began hoarding specie , gold and silver coins . In late December 1861 , banks and then the federal Treasury stopped paying out gold at face value . By mid @-@ 1862 , all federal coins , even the base metal cent , had vanished from co... |
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664 = = Final years , abolition , and collecting = = |
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665 Since gold did not circulate in the United States ( except on the West Coast ) in the postwar period , much of the production of coins of that metal in the United States was double eagles for export . Accordingly , although 1 @,@ 361 @,@ 355 gold dollars were struck in 1862 — the last time production would exceed ... |
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666 In the 1870s and 1880s , public interest grew in the low @-@ mintage gold dollar . Collecting coins was becoming more popular , and a number of numismatists put aside some gold dollars and hoped for increases in value . The Mint most likely channeled its production through some favored Philadelphia dealers , thoug... |
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667 James Pollock , in his final report as Mint Director in 1873 , advocated limiting striking of gold dollars to depositors who specifically requested it . " The gold dollar is not a convenient coin , on account of its small size , and it suffers more proportionately from abrasion than larger coins . " His successors... |
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668 A total of 19 @,@ 499 @,@ 337 gold dollars were coined , of which 18 @,@ 223 @,@ 438 were struck at Philadelphia , 1 @,@ 004 @,@ 000 at New Orleans , 109 @,@ 138 at Charlotte , 90 @,@ 232 at San Francisco and 72 @,@ 529 at Dahlonega . According to an advertisement in the February 1899 issue of The Numismatist , go... |
46.97575378417969 281 WikiText2 |
669 = = Commemorative gold dollars = = |
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670 The gold dollar had a brief resurrection during the period of Early United States commemorative coins . Between 1903 and 1922 nine different issues were produced , with a total mintage of 99 @,@ 799 . These were minted for various public events , did not circulate , and none used Longacre 's design . |
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671 = Johnson – Corey – Chaykovsky reaction = |
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672 The Johnson – Corey – Chaykovsky reaction ( sometimes referred to as the Corey – Chaykovsky reaction or CCR ) is a chemical reaction used in organic chemistry for the synthesis of epoxides , aziridines , and cyclopropanes . It was discovered in 1961 by A. William Johnson and developed significantly by E. J. Corey ... |
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673 The reaction is most often employed for epoxidation via methylene transfer , and to this end has been used in several notable total syntheses ( See Synthesis of epoxides below ) . Additionally detailed below are the history , mechanism , scope , and enantioselective variants of the reaction . Several reviews have ... |
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674 = = History = = |
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675 The original publication by Johnson concerned the reaction of 9 @-@ dimethylsulfonium fluorenylide with substituted benzaldehyde derivatives . The attempted Wittig @-@ like reaction failed and a benzalfluorene oxide was obtained instead , noting that " Reaction between the sulfur ylid and benzaldehydes did not aff... |
183.42352294921875 60 WikiText2 |
676 The subsequent development of ( dimethyloxosulfaniumyl ) methanide , ( CH3 ) 2SOCH2 and ( dimethylsulfaniumyl ) methanide , ( CH3 ) 2SCH2 ( known as Corey – Chaykovsky reagents ) by Corey and Chaykovsky as efficient methylene @-@ transfer reagents established the reaction as a part of the organic canon . |
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677 = = Mechanism = = |
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678 The reaction mechanism for the Johnson – Corey – Chaykovsky reaction consists of nucleophilic addition of the ylide to the carbonyl or imine group . A negative charge is transferred to the heteroatom and because the sulfonium cation is a good leaving group it gets expelled forming the ring . In the related Wittig ... |
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679 The trans diastereoselectivity observed results from the reversibility of the initial addition , allowing equilibration to the favored anti betaine over the syn betaine . Initial addition of the ylide results in a betaine with adjacent charges ; density functional theory calculations have shown that the rate @-@ l... |
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680 The degree of reversibility in the initial step ( and therefore the diastereoselectivity ) depends on four factors , with greater reversibility corresponding to higher selectivity : |
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681 Stability of the substrate with higher stability leading to greater reversibility by favoring the starting material over the betaine . |
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682 Stability of the ylide with higher stability similarly leading to greater reversibility . |
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683 Steric hindrance in the betaine with greater hindrance leading to greater reversibility by disfavoring formation of the intermediate and slowing the rate @-@ limiting rotation of the central bond . |
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684 Solvation of charges in the betaine by counterions such as lithium with greater solvation allowing more facile rotation in the betaine intermediate , lowering the amount of reversibility . |
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685 = = Scope = = |
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686 The application of the Johnson – Corey – Chaykovsky reaction in organic synthesis is diverse . The reaction has come to encompass reactions of many types of sulfur ylides with electrophiles well beyond the original publications . It has seen use in a number of high @-@ profile total syntheses , as detailed below ,... |
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687 = = = Types of ylides = = = |
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688 Many types of ylides can be prepared with various functional groups both on the anionic carbon center and on the sulfur . The substitution pattern can influence the ease of preparation for the reagents ( typically from the sulfonium halide , e.g. trimethylsulfonium iodide ) and overall reaction rate in various way... |
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689 Use of a sulfoxonium allows more facile preparation of the reagent using weaker bases as compared to sulfonium ylides . ( The difference being that a sulfoxonium contains a doubly bonded oxygen whereas the sulfonium does not . ) The former react slower due to their increased stability . In addition , the dialkylsu... |
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690 The vast majority of reagents are monosubstituted at the ylide carbon ( either R1 or R2 as hydrogen ) . Disubstituted reagents are much rarer but have been described : |
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691 If the ylide carbon is substituted with an electron @-@ withdrawing group ( EWG ) , the reagent is referred to as a stabilized ylide . These , similarly to sulfoxonium reagents , react much slower and are typically easier to prepare . These are limited in their usefulness as the reaction can become prohibitively s... |
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692 If the ylide carbon is substituted with an aryl or allyl group , the reagent is referred to as a semi @-@ stabilized ylide . These have been developed extensively , second only to the classical methylene reagents ( R1 = R2 = H ) . The substitution pattern on aryl reagents can heavily influence the selectivity of t... |
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693 If the ylide carbon is substituted with an alkyl group the reagent is referred to as an unstabilized ylide . The size of the alkyl groups are the major factors in selectivity with these reagents . |
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694 The R @-@ groups on the sulfur , though typically methyls , have been used to synthesize reagents that can perform enantioselective variants of the reaction ( See Variations below ) . The size of the groups can also influence diastereoselectivity in alicyclic substrates . |
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695 = = = Synthesis of epoxides = = = |
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696 Reactions of sulfur ylides with ketones and aldehydes to form epoxides are by far the most common application of the Johnson – Corey – Chaykovsky reaction . Examples involving complex substrates and ' exotic ' ylides have been reported , as shown below . |
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697 The reaction has been used in a number of notable total syntheses including the Danishefsky Taxol total synthesis , which produces the chemotherapeutic drug taxol , and the Kuehne Strychnine total synthesis which produces the pesticide strychnine . |
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698 = = = Synthesis of aziridines = = = |
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699 The synthesis of aziridines from imines is another important application of the Johnson – Corey – Chaykovsky reaction and provides an alternative to amine transfer from oxaziridines . Though less widely applied , the reaction has a similar substrate scope and functional group tolerance to the carbonyl equivalent .... |
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