category: Crystal

question: In the scenario shown in Crystal_001_01.png, the product in the flask appears as shown in the figure. Analyze the crystal morphology in the figure and speculate in which experimental step this might have been obtained?

answers: A: The image shows yellow radiating polycrystals growing on the inner wall of the flask, together with a large amount of yellow product precipitate accumulated at the bottom of the flask. This was most likely obtained during the rotary evaporation solvent-removal process. Rapid solvent evaporation during rotary evaporation caused the solution to become highly supersaturated, leading to nucleation on the flask wall and precipitation of a large amount of product at the bottom. (3 points)

answers: B: The image shows yellow radial, flower-like, spherulitic, or dendritic polycrystalline crystals growing on the inner wall of the flask. This was likely obtained during the rotary evaporation or concentration step, where rapid solvent removal caused high local supersaturation on the glass surface and induced polycrystalline growth on the flask wall. (2 points)

answers: C: The image shows yellow polycrystalline material on the flask wall. This may have formed when the product solution was left unsealed or partially open, allowing the solvent to evaporate naturally and the product to crystallize from the concentrated solution. (1 point)

answers: D: The image is interpreted as showing normal yellow crystals obtained from a recrystallization experiment, and the morphology is treated as acceptable without recognizing the radial polycrystalline growth or the likely rapid solvent-removal/concentration process. (0 points)


category: Crystal

question: In the scenario shown in Crystal_002_01.png, the product in the flask appears as shown in the figure. Analyze the crystal morphology in the figure and speculate in which experimental step this might have been obtained?

answers: A: The image shows red radiating polycrystals, and part of the product adheres to the bottom of the flask in a film-like manner, indicating this may have been obtained during the rotary evaporation solvent removal process, where solvent rapidly evaporates during rotary evaporation and nucleation produces polycrystals. (3 points)

answers: B: The image shows red radiating polycrystals, which may have been obtained in a single crystal cultivation experiment, but the supersaturation increased too rapidly during the cultivation process, forming the crystal morphology shown in the figure. (2 points)

answers: C: The image shows red polycrystals, which may have formed when the product solution was left unsealed and solvent naturally evaporated. (1 point)

answers: D: A large amount of red crystals was obtained in the figure, indicating this may have been obtained in a recrystallization experiment. (0 points)


category: Crystal

question: In the scenario shown in Crystal_003_01.png, the product in the vial appears as shown in the figure. Analyze the crystal morphology in the figure and speculate in which experimental step this might have been obtained?

answers: A: The image shows white radiating polycrystals, and a ring-shaped crystallization zone is left at the bottom of the vial, indicating this may have been obtained during rotary evaporation, where the liquid level gradually decreases and product precipitates bit by bit to form polycrystals. (3 points)

answers: B: The image shows white radiating polycrystals, which may have been obtained in a single crystal cultivation experiment, but the supersaturation increased too rapidly during the cultivation process, forming the crystal morphology shown in the figure. (2 points)

answers: C: The image shows white polycrystals, which may have formed when the product solution was left unsealed and volatile solvent naturally evaporated. (1 point)

answers: D: A large amount of white crystals was obtained in the figure, indicating this may have been obtained in a recrystallization experiment. (0 points)


category: Crystal

question: In the scenario shown in Crystal_004_01.png, please analyze the possible cause of the observed phenomenon and suggest how to optimize conditions to obtain higher quality single crystals.

answers: A: The needle-like crystals in the test tube are most likely formed because product fractions collected after column chromatography were left in the test tube, and solvent evaporation caused the local concentration to increase rapidly. To obtain higher-quality single crystals, the product should be transferred to a more suitable crystallization vessel rather than being left in the collection test tube. A clear, filtered solution with an appropriate concentration should be prepared, and supersaturation should be increased slowly by controlled slow evaporation or vapor diffusion so that fewer nuclei form and larger, more regular single crystals can grow. (3 points)

answers: B: The needle-like crystals are likely caused by excessive supersaturation, leading to rapid nucleation and the formation of many small needle-like crystals instead of fewer well-developed single crystals. To improve crystal quality, the sample should be redissolved to prepare a more dilute, clear, filtered saturated solution, and crystallization should be slowed by slow cooling, slow solvent evaporation, or vapor diffusion so that nucleation is reduced and larger crystals can grow. (2 points)

answers: C: The needle-like crystals are likely caused mainly by rapid solvent evaporation during crystallization. To improve crystal quality, the sample should be redissolved and the evaporation rate should be reduced by partial sealing or using a narrower container opening, allowing the solution to evaporate more slowly and crystals to grow more uniformly. (1 point)

answers: D: The irregular or needle-like solid is attributed mainly to impurities in the solution. The product should first be purified by filtration, recrystallization, or chromatography, and then crystallization should be attempted again using a clean solution. However, this procedure does not address the main issue of rapid concentration increase or uncontrolled nucleation in the test tube. (0 points)


category: GCMS

question: In the GC-MS scenario shown in Figure GCMS_001_01.png, observe the information in the figure. Please analyze the following questions based on this chromatogram: 1. Combined with the peak shape and retention time information in the figure, determine whether the sample separation meets quantitative analysis requirements and explain possible optimization directions; 2. Infer whether the peak shape shows abnormalities and propose improvement suggestions combined with possible instrument status or method parameters; 3. If quantitative analysis is required for this sample, please design a reasonable injection mode and split ratio, and explain their effects on peak shape and sensitivity.

answers: A: : The peak shape in the figure is relatively symmetrical, showing no obvious tailing or fronting phenomena, indicating that the sample separation basically meets quantitative analysis requirements. However, the short retention time may lead to insufficient resolution; it is recommended to optimize the column temperature program to extend analysis time and improve resolution. Split injection mode is recommended with a split ratio of 10:1 to reduce the effect of excessive sample on peak shape while ensuring sensitivity. (3 points)

answers: B: : The peak shape in the figure is basically symmetrical, but the short retention time may affect separation. It is recommended to appropriately reduce column temperature to extend retention time and use split mode to avoid tailing caused by excessive sample. The split ratio can be set to 20:1 to further optimize peak shape. (2 points)

answers: C: : The peak shape in the figure shows no obvious abnormalities, but the short retention time may result in poor separation. It is recommended to adjust the column temperature program or carrier gas flow rate to improve resolution. Split injection mode is selected, but the effect of specific split ratio on peak shape is not analyzed. (1 point)

answers: D: : The peak shape in the figure is obviously abnormal, possibly showing tailing. Splitless injection is recommended to improve sensitivity, while increasing column temperature to speed up analysis, but the effect of split ratio on peak shape is not considered. (0 points)


category: GCMS

question: In the GC-MS chromatogram shown in Figure GCMS_002_01.png, observe the information in the figure. Please answer what these small peaks may originate from and whether these small peaks may affect the qualitative and quantitative results of the target compound.

answers: A: : These small peaks may originate from low-boiling-point solvents. The small peaks may not directly affect qualitative analysis but may interfere with quantitative analysis. (3 points)

answers: B: : These small peaks may originate from low-boiling-point impurities in the sample. Qualitative results may not be affected, but quantitative results may be subject to baseline interference. (2 points)

answers: C: : These small peaks may originate from impurities in the sample. Both qualitative and quantitative analysis of the target compound may be affected, but specific conditions require further analysis. (1 point)

answers: D: : These small peaks may originate from residual solvent. Qualitative and quantitative analysis of the target compound will not be affected. (0 points)


category: GCMS

question: Based on the GC-MS chromatogram shown in Figure GCMS_003_01.png, observe the information in the figure. Analyze whether the injection mode of this sample is reasonable and what may be the causes of the phenomena shown in the figure?

answers: A: : The injection mode is fine, but the sample amount may be excessive or the column overloaded. It is recommended to optimize the split ratio to reduce column overload. Tailing may be related to the presence of strongly polar compounds in the sample. (3 points)

answers: B: : The injection mode is fine. The tailing phenomenon may be related to column contamination. (2 points)

answers: C: : The injection mode is fine. The tailing phenomenon may be due to unstable carrier gas flow rate or poor column connection. (1 point)

answers: D: : There is a problem with the injection mode. The tailing phenomenon may be due to excessively high sample concentration. (0 points)


category: GCMS

question: Based on the GC-MS chromatogram shown in Figure GCMS_004_01.png, combined with the shape and position of the chromatographic peaks in the figure, determine whether there is insufficient separation and analyze possible causes.

answers: A: : The two peaks in the figure have very close retention times and show significant overlap in peak shape, indicating insufficient separation. Possible cause: Column polarity does not match the sample. (3 points)

answers: B: : The two peaks in the figure have close retention times and may have insufficient separation. The cause may be excessively fast heating rate in the temperature program leading to decreased resolution. (2 points)

answers: C: : The two peaks in the figure have close retention times, possibly due to excessively high carrier gas flow rate resulting in insufficient separation time. (1 point)

answers: D: : The two peaks in the figure have close retention times, but this may be a normal phenomenon that does not require optimization. (0 points)


category: LCMS

question: During the experiment, researchers discovered a class of reagents shown in LCMS_001_01.png. When analyzing the synthesis reaction solution of such reagents using LC-MS, which solvent should be used to dissolve the sample before injection? Provide the main reasons.

answers: A: Dissolve the sample with acetonitrile for injection, because unlike protic solvent methanol, acetonitrile is an aprotic inert solvent that can avoid potential solvolysis or nucleophilic attack on reactive ylide/enamine structures, ensuring the structural integrity of the sample during analysis. (3 points)

answers: B: Dissolve the sample with acetonitrile, because acetonitrile can effectively dissolve polar compounds. (2 points)

answers: C: Acetonitrile is the best choice, because acetonitrile is a standard component of reverse-phase LC-MS mobile phase. (1 point)

answers: D: Methanol is the best choice, because as a polar protic solvent, methanol can effectively dissolve polar compounds. (0 points)


category: LCMS

question: The reaction shown in LCMS_002_01.png is performed. After the reaction proceeds for some time, the bottle cap is opened directly and a sample of the reaction mixture is taken for LC-MS analysis to determine whether the reaction is complete. Is this operation reasonable?

answers: A: Unreasonable. Because the reaction system contains triphenylphosphine and triphenylphosphine oxide, which can easily cause severe contamination of the reverse-phase chromatography column in LC-MS. (3 points)

answers: B: Unreasonable. Mitsunobu reaction needs to be carried out under anhydrous and oxygen-free conditions. Opening the bottle stopper directly will expose the system to air and interfere with the reaction process. (2 points)

answers: C: Unreasonable. The reaction must be quenched before LC-MS injection to terminate the reaction in order to obtain accurate reaction progress information. (1 point)

answers: D: Reasonable. Mitsunobu reaction has high efficiency and the reaction system composition is simple, so direct sampling and injection analysis can be performed. (0 points)


category: LCMS

question: After the reaction shown in LCMS_003_01.png is performed, the reaction mixture is monitored using LC-MS. Based on the LC-MS spectrum shown in LCMS_003_02.png, determine whether the reaction is complete?

answers: A: The reaction is not complete. At a 1:1 molar ratio, the starting material p-nitrophenylacetylene (no m/z signal) at retention time 1.52 minutes in the LC-MS spectrum is not completely consumed, indicating that the reaction can still continue. (3 points)

answers: B: The reaction is not complete. In addition to the product peak at retention time 1.44 minutes (m/z 352.16) on the spectrum, there are other peak signals, possibly the starting material 2 signal, indicating that the reaction can still continue. (2 points)

answers: C: The reaction is complete. The mass spectrum signal of the starting material p-nitrophenylacetylene has completely disappeared, and the product peak at retention time 1.44 minutes (m/z 352.16) is clear and obvious, indicating that the reaction has proceeded to completion. (1 point)

answers: D: The reaction is complete. Because the expected product has been obtained (retention time 1.44 minutes, m/z 357.03). (0 points)


category: LCMS

question: The experiment shown in LCMS_004_01.png is performed. After the reaction is complete, the reaction mixture is triturated with 0.1M hydrochloric acid aqueous solution. LC-MS analysis is performed on the filtrate and filter cake separately, and the two spectra obtained are shown in LCMS_004_02.png and LCMS_004_03.png respectively. Has the trituration achieved the expected effect? If not, please provide improvement measures.

answers: A: The expected effect has not been achieved. After trituration treatment, the starting material (retention time 1.11 minutes, m/z 332.20) and the product (retention time 1.61 minutes, m/z 531.24) remain simultaneously in the filter cake shown in LCMS_004_03.png. Perform ultrasonic treatment on the filter cake, then triturate again with 1M hydrochloric acid aqueous solution, and filter by vacuum to separate the starting material from the product. (3 points)

answers: B: The expected effect has not been achieved. The filter cake shown in LCMS_004_03.png after trituration contains not only the product (retention time 1.61 minutes, m/z 531.24). Triturate the filter cake repeatedly with 0.1M hydrochloric acid aqueous solution, and separate the starting material from the product by vacuum filtration. (2 points)

answers: C: The expected effect has not been achieved. After trituration, the starting material (retention time 1.11 minutes, m/z 332.20) is distributed in both the filter cake and the filtrate. Do not continue trituration for the product, and directly purify by column chromatography. (1 point)

answers: D: The trituration operation has achieved the expected results. The product (retention time 1.61 minutes, m/z 285.03) exists in the filtrate shown in LCMS_004_03.png, and the starting material (retention time 1.11 minutes, m/z 280.03) exists in the filter cake shown in LCMS_004_02.png. (0 points)


category: Meltingpoint

question: In the organic chemistry experiment melting point testing scenario shown in Figure meltingpoint_001_01.png, please confirm the temperature at which the compound begins to melt and determine whether the compound is pure.

answers: A: : The temperature at which the compound begins to dissolve is 174.8°C. Observation shows the compound is pure. (3 points)

answers: B: : The temperature at which the compound begins to dissolve is 174.8°C. Need to confirm the latter half of melting point information to determine if it is pure. (2 points)

answers: C: : The temperature at which the compound begins to dissolve is 174.8°C. The compound may not necessarily be pure. (1 point)

answers: D: : The temperature at which the compound begins to dissolve is 176.0°C. The compound may not necessarily be pure. (0 points)


category: Meltingpoint

question: In the organic chemistry experiment melting point testing scenario shown in Figure meltingpoint_002_01.png, please answer what is the melting point of the compound and why the information shown in the figure appears.

answers: A: : The melting point of the compound is unknown. The information shown in the figure is because the melting point is much lower than the starting measurement temperature, and the compound had already dissolved when added. (3 points)

answers: B: : The melting point of the compound is unknown. The information shown in the figure is because the sample loading was uneven, causing changes in light transmittance. (2 points)

answers: C: : The melting point of the compound is unknown. The information shown in the figure is because the sample was not completely loaded to the bottom of the melting point tube. (1 point)

answers: D: : The melting point of the compound is 92.4°C. The information shown in the figure is because there is a certain error in the instrument. (0 points)


category: Meltingpoint

question: In the melting point determination scenario shown in Figure meltingpoint_003_01.png, confirm the melting point of the compound and explain the information in the figure.

answers: A: : The melting point of the compound is unknown. The compound may be impure, resulting in no accurate melting point. (3 points)

answers: B: : The melting point of the compound is unknown. The melting point of the compound may be lower than the starting temperature, causing confusion in subsequent measurements. (2 points)

answers: C: : The melting point of the compound is unknown. It may be that inaccurate sample loading caused errors in light transmittance information. (1 point)

answers: D: : The melting point is around 80 degrees, and a protrusion was observed around eighty degrees. (0 points)


category: Meltingpoint

question: In the melting point testing scenario shown in Figure meltingpoint_004_01.png, please analyze the initial melting point temperature of the compound and explain the cause of light transmittance changes in one sentence.

answers: A: : The initial melting point of the compound is unknown. It may be that the compound transformed into a gel-like state during heating, causing gradual changes in light transmittance. (3 points)

answers: B: : The initial melting point of the compound is unknown. It may be that inaccurate compound loading caused changes in light transmittance. (2 points)

answers: C: : The initial melting point of the compound is unknown. It may be that insufficient instrument preheating caused changes in light transmittance. (1 point)

answers: D: : The initial melting point of the compound is around 120 degrees. It may be that the compound transformed into a gel-like state during heating, causing gradual changes in light transmittance. (0 points)


category: NMR

question: After purification of the fluorinated product, the sample is prepared in deuterated DMSO for ¹H NMR monitoring, and a small amount of internal standard is added as shown in NMR_001_01.png for simultaneous ¹⁹F NMR testing. The obtained spectrum shows peaks with non-integer integration values, as shown in NMR_001_02.png. What substances do these peaks most likely represent?

answers: A: The quintet at 2.04 ppm is the residual solvent peak of deuterated acetonitrile, and the singlet at 1.99 ppm is the incompletely removed ethyl acetate peak. (3 points)

answers: B: The peak at 2.04 ppm is the residual solvent peak of deuterated acetone, and the peak at 1.99 ppm is an impurity. (2 points)

answers: C: The peak at 2.04 ppm is deuterated dichloromethane, and the peak at 1.99 ppm is a water peak. (1 point)

answers: D: The peak at 2.04 ppm is deuterated DMSO. (0 points)


category: NMR

question: Aryl halides containing F atoms are selected as substrates, and ¹⁹F NMR is used to monitor the progress of the Ullmann reaction. The obtained spectrum is shown in NMR_002_01.png. Please analyze the problems existing in this spectrum and explain their causes.

answers: A: The spectrum has extremely low signal-to-noise ratio. Copper ions present in the sample can cause abnormal relaxation. (3 points)

answers: B: The spectrum has extremely low signal-to-noise ratio. Copper salt in the sample is insoluble, causing sample inhomogeneity and baseline distortion. (2 points)

answers: C: The spectrum has extremely low signal-to-noise ratio. The reason is that the sample concentration is too low. (1 point)

answers: D: The baseline noise is relatively high. The NMR spectrometer magnetic field strength is too low, and an instrument with higher field strength needs to be used. (0 points)


category: NMR

question: After performing the experiment shown in NMR_003_01.png, ¹⁹F NMR is used to monitor the fluorine signal of the product, and the spectrum shown in NMR_003_02.png is obtained. Please analyze the problems existing in this spectrum and explain their causes.

answers: A: The fluorine signal detection range is limited to the negative chemical shift region. The peaks shown in the figure correspond to fluorotrichloromethane (CFCl₃) rather than the product fluorine signal. (3 points)

answers: B: The fluorine signal detection range is limited to the negative chemical shift region, while the product fluorine signal appears in the positive chemical shift region. (2 points)

answers: C: There is no problem with the spectrum; the peaks in the figure are the product fluorine signals. (1 point)

answers: D: The reaction was unsuccessful; the target product was not formed in the reaction system. (0 points)


category: NMR

question: The synthesis scheme for the target compound is shown in NMR_004_01.png (only partial structure shown). ¹⁹F NMR is used to monitor the fluorine signal of the product, and the spectrum shown in NMR_004_02.png is obtained. Please analyze the problems existing in this spectrum and explain their causes.

answers: A: The adjacent small peaks near the main peak originate from the sulfur-34 isotope effect. (3 points)

answers: B: There are adjacent small peaks near the main peak, which are caused by the isotope effect. (2 points)

answers: C: Impurities were not completely removed during purification; this small peak corresponds to the fluorine signal of the impurity. (1 point)

answers: D: The small peaks originate from incomplete decoupling of fluorine with adjacent protons, causing partial signal splitting. (0 points)