category: Column

question: The UV curve of the automated column chromatography purification system is shown in column_001_01.png, and the collection tubes are shown in column_001_02.png. Compare the condition of collection tube No. 18 in both figures and analyze what substance might have been collected in this tube.

answers: A: Possible collection of impurities such as natural product pigments or inorganic complexes. The liquid in tube No. 18 appears light pink with no UV absorption at 254/280 nm, indicating the absence of an aromatic conjugated system. (3 points)

answers: B: Possible collection of impurities from the column chromatography elution solvent. The fraction in tube No. 18 shows no UV absorption, but a light pink substance is visible to the naked eye. (2 points)

answers: C: The colored liquid in tube No. 18 indicates that the substance in this tube is the target product. The weak UV signal and light color are due to low concentration. (1 point)

answers: D: Tube No. 18 is a blank solvent tube containing only eluent and should be treated as waste liquid. (0 points)


category: Column

question: During the column chromatography elution process shown in column_002_01.png, the phenomenon depicted in the figure was observed. Analyze the possible causes and propose improvement strategies.

answers: A: Tailing may be caused by excessive adsorption of the sample on the stationary phase due to insufficient polarity of the solvent system. This can be improved by gradient elution with gradual increase in the proportion of high-polarity solvent. (3 points)

answers: B: Tailing may be caused by sample overloading. Try reducing the sample concentration to improve separation. (2 points)

answers: C: Tailing may be related to stationary phase selection; it is recommended to try different packing materials. (1 point)

answers: D: The overlap of two absorption peaks may be due to the similar polarity of the two substances causing close elution times and resulting in overlap. (0 points)


category: Column

question: The UV curve of the automated column chromatography purification system is shown in column_003_01.png. After separation, unknown signals appeared in the NMR spectrum of the product. What is the most likely cause of this situation? How should the conditions be adjusted?

answers: A: Sample overloading caused peak broadening and significantly reduced column separation efficiency, leading to collection of impurities. Optimization method: strictly control the sample loading amount. (3 points)

answers: B: The UV detector signal was saturated, masking the small peaks of subsequent impurities. A non-maximum absorption wavelength should be selected for re-monitoring. (2 points)

answers: C: The elution polarity of the column chromatography was insufficient, causing product tailing and resulting in collection of impurities. Gradient elution should be used to gradually increase the eluent polarity. (1 point)

answers: D: Product decomposition occurred during column chromatography, causing the appearance of unknown signals. Different eluents or column packing materials should be used to avoid decomposition. (0 points)


category: Evaporation

question: Before performing column chromatography, dry loading is required. After adding silica gel to the sample solution and performing prolonged rotary evaporation, the silica gel appears as shown in Evaporation_001_01.png. What should be done to ensure subsequent experimental procedures proceed normally?

answers: A: Add a low-polarity co-solvent, add an appropriate amount of silica gel and mix thoroughly, then continue rotary evaporation. (3 points)

answers: B: Use an oil pump to achieve deeper vacuum to facilitate removal of residual solvent. (2 points)

answers: C: Extend rotary evaporation time under current water bath temperature and vacuum conditions. (1 point)

answers: D: Increase the water bath temperature of the rotary evaporator and continue rotary evaporation. (0 points)


category: Evaporation

question: After extracting the product with ethyl acetate, the solvent is removed under reduced pressure. Rotary evaporation parameters are shown in Evaporation_002_01.png. However, after a long time, the system still remains in the state shown in Evaporation_002_02.png. Analyze possible causes and propose methods to improve experimental efficiency.

answers: A: The water bath temperature is only 25°C, and the pressure gauge reads 150 Torr. The current temperature and vacuum level do not meet the requirements for efficient removal of ethyl acetate. The water bath temperature should be increased to above 30°C, while the vacuum should be deepened to approximately 90 Torr; subsequently, continue to increase water bath temperature and vacuum level. (3 points)

answers: B: The system pressure is maintained at 150 Torr, which is insufficient vacuum for ethyl acetate evaporation. The pressure should be reduced below 80 Torr. (2 points)

answers: C: The water bath temperature is only 25°C, which cannot provide sufficient heat for efficient ethyl acetate evaporation. It should be increased above 45°C. (1 point)

answers: D: The rotary evaporator rotation speed is too fast, causing large amounts of ethyl acetate to adhere to the flask walls without forming an effective liquid film, producing only physical dispersion and thus hindering evaporation. (0 points)


category: Evaporation

question: Before performing column chromatography, dry loading is required. After adding silica gel to the sample solution and performing rotary evaporation, the situation shown in Evaporation_003_01.png occurred. Analyze the cause and explain how to avoid this situation.

answers: A: During rotary evaporation, the vacuum was applied too quickly and the water bath temperature was too high, causing bumping that carried silica gel powder splashing. Cotton plugs should be placed in the anti-splash guard to prevent silica gel from being drawn into the tubing. (3 points)

answers: B: During rotary evaporation, the vacuum increased too rapidly and the water bath temperature was high, causing solvent bumping. A slow vacuum application, low rotation speed, low temperature startup procedure should be adopted, with parameters adjusted gradually to prevent bumping. (2 points)

answers: C: The water bath temperature was too high, causing violent solvent boiling; the water bath temperature setting should be reduced. (1 point)

answers: D: The rotary evaporator rotation speed was too slow, causing silica gel to accumulate and cake at the bottom of the flask. The rotation speed should be increased. (0 points)


category: Extraction

question: During the extraction process, the situation shown in Extraction_001_01.png is observed. What is the best operation to solve this problem?

answers: A: Add a small amount of saturated brine to break the emulsion through the salting-out effect. (3 points)

answers: B: Gently shake the separatory funnel and use a glass rod to help break the interfacial film. (2 points)

answers: C: Allow to stand for an extended period to wait for layer separation. (1 point)

answers: D: Vigorously shake the emulsion and heat the separatory funnel to 40°C to accelerate layer separation. (0 points)


category: Extraction

question: The compound is shown in Extraction_002_01.png. The aqueous mixture is extracted with dichloromethane, shaken thoroughly, and allowed to stand for layer separation. Which layer should be monitored next?

answers: A: The lower layer, because benzoic acid has greater solubility in dichloromethane than in water, and dichloromethane has greater density than water. (3 points)

answers: B: Both layers should be monitored, because benzoic acid has certain solubility in both DCM and water. (2 points)

answers: C: The lower layer, because benzoic acid has greater solubility in dichloromethane than in water. (1 point)

answers: D: The upper layer, because benzoic acid has lower solubility in dichloromethane than in water, and dichloromethane has lower density than water. (0 points)


category: Extraction

question: DMF is used as the reaction solvent. After reaction completion, the mixture is monitored by LC-MS; the spectrum is shown in Extraction_003_01.png. How should this be handled subsequently?

answers: A: Re-extract the aqueous phase with ethyl acetate three times, then perform LC-MS analysis. The final product peak appears only in the organic phase. (3 points)

answers: B: Extract with other organic solvents and perform LC-MS analysis; the final product peak appears only in the organic phase. (2 points)

answers: C: Mix the organic and aqueous phases, re-extract, and then proceed directly with subsequent operations. (1 point)

answers: D: Remove the organic phase by rotary evaporation, then proceed directly with subsequent steps. (0 points)


category: Lyophilized

question: In the freeze-dried product shown in Figure lyophilized_001_01.png, analyze the following question: 1. Did any operational problems or improper parameter settings occur during the sample freeze-drying process?

answers: A: : From the sample state analysis, the sample is in powder form with no operational problems, which is a normal post-freeze-drying state. Therefore, it is inferred that there are no operational problems. (3 points)

answers: B: : From the sample state analysis, the sample is in powder form with no operational problems, which is a normal post-freeze-drying state. Possible operational problem: excessive sample loading, resulting in prolonged freeze-drying time. (2 points)

answers: C: : From the sample state analysis, the sample shows uneven distribution. Possible operational problem: insufficient temperature setting during the pre-freezing stage of the freeze-dryer, causing the sample to not freeze completely. (1 point)

answers: D: : From the sample state analysis, sample agglomeration may be caused by insufficient temperature during the pre-freezing stage or excessive vacuum during the sublimation stage. Improvement methods include increasing the pre-freezing temperature and reducing the vacuum, but the influence of sample loading thickness on drying uniformity was not considered in detail. (0 points)


category: Lyophilized

question: In the organic chemistry experiment freeze-drying operation scenario shown in Figure lyophilized_002_01.png, what is the most likely cause of the situation shown in the figure?

answers: A: : The sample was not fully frozen during liquid nitrogen freezing, resulting in incomplete freezing of the sample. (3 points)

answers: B: : Caused by insufficient cold trap temperature. (2 points)

answers: C: : Sample overflow may be related to excessive sample loading, and there may also be a problem of excessively high vacuum setting during the sublimation stage. (1 point)

answers: D: : The sample structure was unstable during the solution sublimation process, causing sample overflow. (0 points)


category: Lyophilized

question: In the organic chemistry experiment freeze-drying operation scenario shown in Figure lyophilized_003_01.png, analyze whether the current instrument status allows freeze-drying operation? If the status is abnormal, how should it be operated?

answers: A: : The display shows normal temperature but insufficient pressure value. Subsequent operation: wait for ten minutes, if pressure decreases, freeze-drying operation can proceed. (3 points)

answers: B: : The display shows normal temperature but insufficient pressure value. Subsequent operation: check if there is air leakage at the black rubber ring interface. (2 points)

answers: C: : The display shows normal temperature but insufficient pressure value. Subsequent operation: check if other outlets are completely closed. (1 point)

answers: D: : The cold trap temperature and vacuum display are normal, and freeze-drying operation can proceed directly. (0 points)


category: Recrystallization

question: In the organic chemistry experiment recrystallization operation scenario shown in Figure Recrystallization_001_01.png, please analyze the following questions: 1. Based on the information in the figure, determine whether there are any abnormal phenomena currently present, and speculate on possible causes; 2. If abnormalities exist, please propose specific improvement measures; 3. Combined with the information in the figure, explain how to optimize subsequent operations to improve crystal purity.

answers: A: : Undissolved compound exists in the flask in the figure, indicating an error in the first step of solvent selection with poor solubility. It is recommended to improve the recrystallization method by first heating and raising the temperature, then slowly cooling down, and re-evaluating the solvent system to select a solvent more suitable for the target compound to optimize the solubility difference. In addition, the connection standardization of the suction filtration device needs to be checked to ensure good fit between the filter paper and funnel to avoid overly wet filter cake. During washing, a small amount of cold solvent should be used to avoid dissolving crystals. (3 points)

answers: B: : Undissolved compound exists in the flask in the figure, indicating an error in the first step of solvent selection with poor solubility. It is recommended to extend the cooling time and use ice bath assistance, while checking whether the solvent system is suitable for the solubility difference of the target compound. During suction filtration, attention should be paid to filter paper fit, and cold solvent should be used for washing to reduce crystal dissolution and ensure complete transfer of crystals to the filter paper to minimize product loss. (2 points)

answers: C: : Undissolved compound exists in the flask in the figure, indicating an error in the first step of solvent selection with poor solubility. It is recommended to treat the mother liquor with activated carbon decolorization and optimize the suction filtration device connection to improve filter cake quality. (1 point)

answers: D: : Crystal morphology in the flask in the figure indicates that recrystallization is complete, and no further optimization is needed. The current device can be used directly during suction filtration. (0 points)


category: Recrystallization

question:
In the organic chemistry experiment recrystallization operation scenario shown in Figure Recrystallization_002_01.png, please analyze the following questions based on the phenomena shown in the figure:
1. Which stage is the current recrystallization operation in?
2. What problems are reflected by the state in the figure?
3. Based on the phenomena in the figure, propose at least two improvement strategies to optimize the recrystallization effect, and explain their principles.

answers: A: : Current operation may be at the stage of adding solvent for dissolution. Undissolved white solid can be observed on the side of the flask, indicating that the selected solvent is not the best solvent. Improvement strategies include: (1) Re-selecting the solvent system to ensure the target compound fully dissolves at high temperature and solubility significantly decreases at low temperature; (2) Controlling the cooling rate, for example first naturally cooling at room temperature, then transferring to ice bath to avoid oily substance precipitation; (3) Adding a small amount of activated carbon before dissolution to remove impurities and reduce oily substance formation during crystallization. The principles of the above strategies are optimizing the solvent system and cooling conditions to improve crystal purity and morphology. (3 points)

answers: B: : Current operation may be at the crystallization stage, irregular crystal morphology in the flask and darker mother liquor color may be due to incomplete impurity removal or unreasonable cooling conditions. Improvement suggestions include: (1) Trying to change the solvent system to improve dissolution and crystallization efficiency of the target compound; (2) Performing hot filtration before cooling to remove insoluble impurities. The above methods can improve crystal purity to some extent, but experimental conditions may need further optimization. (2 points)

answers: C: : Current operation may be at the crystallization stage, irregular crystal morphology in the flask. This may be due to insufficient cooling or solvent evaporation. Improvement suggestions include: extending cooling time or replenishing solvent, but how to solve the oily substance problem is not clearly specified. (1 point)

answers: D: : Current operation may be at the cooling crystallization stage, crystal morphology is normal. Further optimization can consider selecting greener solvents to reduce pollution. (0 points)


category: Trituration

question: In the trituration-related scenario shown in Figure Trituration_001_01.png, please analyze the following questions based on this figure, analyze possible causes, and propose two improvement strategies to optimize the trituration purification effect.

answers: A: : The amount of solvent used is insufficient to completely dissolve all products, causing some products to remain in solid form. The amount of solvent can be increased to ensure all target products are dissolved, or a small amount of solvent with better solubility can be added to ensure complete dissolution of the product. (3 points)

answers: B: : The amount of solvent used is insufficient to completely dissolve all products, causing some products to remain in solid form. The temperature can be appropriately increased to ensure complete dissolution of target products, then cool down for trituration, referring to recrystallization treatment methods, or a small amount of solvent with better solubility can be added to ensure complete dissolution of the product. (2 points)

answers: C: : It may be due to improper solvent selection, causing impurities and products to co-deposit. When selecting preferred solvents, the solubility differences of impurities should be considered, choosing solvents where the product is slightly soluble while impurities are soluble. Meanwhile, control the trituration temperature within a range below the solvent boiling point to avoid uneven deposition caused by rapid solvent volatilization. The stirring method should ensure uniform slurry distribution to avoid local supersaturation. (1 point)

answers: D: : The deposits may be due to excessively high trituration temperature causing rapid solvent volatilization. You can try lowering the trituration temperature or selecting solvents with higher boiling points. Meanwhile, avoid local supersaturation phenomena during stirring. (0 points)


category: Trituration

question: In the trituration-related scenario shown in Figure Trituration_002_01.png, please analyze the following questions based on this figure, analyze the possible causes of this phenomenon, and propose strategies to optimize the trituration purification effect. Explain how to improve the purification effect by adjusting these conditions.

answers: A: : There is a problem with the size of the selected flask. Under the premise of ensuring experimental operation safety, choose the smallest possible flask for trituration to reduce product adhesion to the flask wall, which leads to poor results. Subsequently, the flask can be replaced and the operation can be repeated without changing the current reagent amounts. (3 points)

answers: B: : There is a problem with the magnetic stirrer selected for the experiment. A stirrer should be chosen that can agitate the entire reaction liquid while ensuring that the trituration compound does not splash. When selecting a magnetic stirrer, the size of the stirrer should be compatible with the flask size to ensure the stirrer can completely cover the bottom of the flask, thereby ensuring the trituration effect. Subsequently, the magnetic stirrer can be replaced and the operation can be repeated without changing the current reagent amounts. (2 points)

answers: C: : The suspended state of solid product in the figure may be due to insignificant solubility differences between the solvent and the product, resulting in ineffective impurity removal. Optimization strategies include selecting more suitable solvents to make the product slightly soluble while impurities are soluble, increasing solid-liquid ratio to improve mass transfer efficiency, using stronger stirring to promote uniform contact, and reducing product dissolution through low temperature control. (1 point)

answers: D: : It may be due to insufficient solvent amount. You can increase the solvent amount to improve the suspended state. However, the selective dissolution capacity of the solvent and the effect of stirring are not considered. (0 points)


category: Trituration

question: In the trituration-related scenario shown in Figure Trituration_003_01.png, please analyze the following questions based on this figure. It is known that this product is slightly soluble in solvent n-hexane, while the main impurity is easily soluble in solvent n-hexane. The experimenter found that after trituration, it still appears as shown in the figure. Please analyze the most likely cause and propose an improvement plan.

answers: A: : Improper operation, using a glass rod for trituration, resulting in insufficient stirring and incomplete impurity dissolution. Improvement plan: Use a magnetic stirrer to ensure sufficient stirring. (3 points)

answers: B: : Improper operation, using a glass rod for trituration, resulting in insufficient stirring and incomplete impurity dissolution. Improvement plan: Add one drop of solvent with good solubility for the product to achieve the effect of first dissolving, then precipitating. (2 points)

answers: C: : The dissolving capacity of n-hexane for impurities is insufficient, resulting in insufficient impurity dissolution. Improvement plan: Select a solvent with higher solubility for impurities and increase the amount of solvent used. (1 point)

answers: D: : It may be due to improper solvent selection resulting in incomplete impurity removal. The improvement plan is to try using other solvents. The expected effect is that the product color may be improved. (0 points)


category: TLC

question: In the experiment, an attempt was made to extend the Mitsunobu reaction to more nucleophilic substrate materials. The structure of the catalyst BEHT triflate used is shown in TLC_001_01.png. After spotting the reaction mixture onto the TLC plate, the obtained data is shown in TLC_001_02.png. Please analyze the possible cause of the abnormal spot morphology and provide specific operable solutions.

answers: A: The Mitsunobu reaction system contains polar alcohol substrates as well as nucleophilic reagents such as alcohols, phenols, carboxylic acids, and amines, which are easily adsorbed by silica gel. Solution: Add trace amounts of triethylamine or acetic acid to the developing solvent to suppress silica gel adsorption. (3 points)

answers: B: The Mitsunobu reaction system contains polar alcohol substrates as well as nucleophilic reagents such as alcohols, phenols, carboxylic acids, and amines, which are easily adsorbed by silica gel. Solution: Increase the polarity of the developing solvent to force elution. (2 points)

answers: C: The sample is severely overloaded, causing tailing. Solution: Reduce the spotting amount. (1 point)

answers: D: The catalyst used in the reaction is a strongly polar salt, which easily tails on silica gel plates. (0 points)


category: TLC

question: When using the compound shown in TLC_002_01.png as a base for nucleophilic substitution reactions, two rounds of thin-layer chromatography were performed, obtaining the results shown in TLC_002_02.png and TLC_002_03.png respectively. Please compare the two TLC results and explain the cause of this phenomenon.

answers: A: The silica gel surface is rich in weakly acidic silanol groups. Basic amine compounds undergo adsorption with silica gel, resulting in severe tailing. For the second spotting, 1% triethylamine was added, enabling amine compounds to migrate normally and form symmetrical, rounded spots. (3 points)

answers: B: Basic amine compounds undergo adsorption on the silica gel surface, causing tailing. From the migration behavior, the developing solvent system polarity was stronger in the second spotting, improving the tailing situation. (2 points)

answers: C: The spotting amount was smaller in the second spotting, causing the originally tailed spots to become compact circular spots. (1 point)

answers: D: Neutral alumina plates were selected for the second plate spotting to avoid tailing. (0 points)


category: TLC

question: When monitoring the Suzuki cross-coupling reaction, TLC analysis obtained the results shown in TLC_003_01.png; after 2 hours of reaction, TLC analysis was performed again under the same conditions, obtaining the results shown in TLC_003_02.png. Based on the observed dynamic changes, determine whether the reaction has reached completion at this time and provide reasons.

answers: A: TLC analysis shows that the boronic acid starting material has been completely consumed, the product spot intensity has reached a plateau, while residual aryl halide still exists. Since the boronic acid starting material is the limiting reagent, even if unreacted aryl halide remains, the reaction can be judged as complete. (3 points)

answers: B: The product spot intensity no longer increases and the boronic acid starting material disappears, indicating that the coupling reaction has stopped. However, due to residual aryl halide, in a strict sense the conversion is not complete, and additional boronic acid raw material should be added to promote complete conversion. (2 points)

answers: C: Although the boronic acid starting material is no longer visible in TLC, it may undergo self-coupling to form by-products. Residual aryl halide and unchanged product intensity may also indicate catalyst deactivation and that the reaction has not reached chemical equilibrium. (1 point)

answers: D: The new spot is more likely to come from self-coupling of boronic acid rather than the desired cross-coupling product, indicating that the reaction has not proceeded effectively. (0 points)