Instrumental Analysis Practice Questions (Organic Chemical Engineering)

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Ultraviolet-Visible Absorption Spectroscopy (20 points in total)
I. Multiple-choice questions (1 point per question, 5 points in total)
1. The wavelength range of near-ultraviolet light is ( )
A. 400–750 nm
B. 10–200 nm
C. 200–400 nm
D. >750 nm

2. What affects the value of the molar absorptivity ε? ( )
A. The concentration of the absorbing substance
B. The length of the absorption cell
C. The wavelength of the incident light
D. The intensity of the incident light

3. To increase the sensitivity of spectrophotometric analysis, one can do the following:
A. Increase the concentration
B. Increase the wavelength of the incident light
C. Increase the molar absorptivity ε
D. Increase the amplification factor of the instrument for light signals

4. If the transmittance of a colored solution is 20%, then its absorbance is ( )
A. -lg0.80
B. -lg0.20
C. -lg80
D. -lg20

5. When measuring the absorbance of a colored solution, if an absorbance of A is obtained using a 1 cm cuvette, then what will be the absorbance when using a 2 cm cuvette? ( )
A. 2A
B. A/2
C. A
D. 4A

II. Fill-in-the-blank questions (1 point per blank, 7 points in total)
1. Ultraviolet-visible absorption spectroscopy corresponds to the excitation transitions between molecular energy levels, while infrared absorption spectroscopy also corresponds to such excitation transitions. 2. When the concentration of the absorbing substance at λmax is doubled, ε will . 3. In an ultraviolet-visible spectrophotometer, the incident light, sample cell, and detector are generally in a certain relationship. 4. The absorption spectrum curve is a graph of versus , and its purpose is . III. Calculation (4 points) After 1.000 g of steel sample is dissolved in nitric acid, potassium periodate is used to oxidize the manganese present therein to permanganate ions. Diluted to 250 ml in a volumetric flask, the measured absorbance was 16% of that of 0.001000 mol.L-1 KMnO4. Try to calculate the percentage content of manganese in the steel sample. (MMn=55) IV. Proposed structure (4 points) A trienic compound with the structural formula ; upon partial hydrogenation, two compounds are obtained. One of these compounds exhibits an absorption peak at 235 nm in its ultraviolet spectrum, and its structural formula is ； Another one has an absorption peak at 275 nm, and its structural formula is . Chromatography (30 points in total)
I. Multiple-choice questions (10 points in total, 2 points per question)
1. In gas chromatography, the retention data recorded in literature can be used for qualitative analysis. Which of the following is the most useful for this purpose? ( )
A: Adjusted retention volume
B: Relative retention value
C: Retention index
D: Both relative retention value and retention index

2. The method used by Tswett to separate plant pigments using petroleum ether as the eluent was ( )
A: LLC
B: LSC
C: SEC
D: IEC

3. The parameter used for quantification in chromatography is ( )
A: Retention time
B: Relative retention value
C: Half-width at half maximum
D: Peak area

4. Among the following quantification methods, which one does not use a correction factor (f)? ( )
A: External standard method
B: Internal standard method
C: Normalization method

5. When using a TCD detector, the carrier gas commonly used to improve its sensitivity is ( )
A: N2
B: H2
C: Ar

II. Fill-in-the-blank questions (16 points in total, 2 points per blank)
1. For the same component, the detector’s response value is proportional to , and this is the basis for quantitative analysis in chromatography. 2. The carrier gases used in gas chromatography generally include , etc. 3. The upper limit of column temperature in gas-liquid chromatography depends on. 4. To address the “general problems of elution chromatography,” techniques are commonly used in gas chromatography, while techniques are often employed in liquid chromatography. 5. Compared with gas chromatography, liquid chromatography is not restricted by the sample and is highly suitable for separating compounds with high boiling points, strong polarity, and poor thermal stability. III. Calculation problem (4 points) GLC was used to separate n-pentane and propene, and the following chromatographic data were obtained: Component, Air, n-Pentane, Propene; t’R/min: 0.75, 5.35, 2.45. Calculate the relative retention value γ_propene/n-pentane and the separation factor (α). Infrared Spectroscopy and Nuclear Magnetic Resonance Spectroscopy (40 points in total)
I. Multiple-choice questions (1 point per question, 5 points in total)
1. Among the carbonyl compounds ① RCOR, ② RCOCl, ③ RCOH, and ④ RCOF, which one has the highest C=O stretching vibration frequency? ( )
A. ①
B. ②
C. ③
D. ④

2. In alcohol compounds, the O-H stretching vibration frequency shifts to lower wavenumbers as the solution concentration increases. What is the reason for this? ( )
A. The polarity of the solution increases.
B. Intermolecular hydrogen bonding becomes stronger.
C. The induction effect increases.
D. Vibrational coupling is more likely to occur.

3. A certain compound shows a weak absorption at 270 nm in the ultraviolet region. Its infrared spectrum exhibits absorption peaks at 2700–2900 cm⁻¹ and 1725 cm⁻¹. What could this compound be? ( )
A. Aldehyde
B. Alcohol
C. Carboxylic acid
D. Ester

4. Nuclear magnetic resonance spectroscopy provides information about molecular structure through the characteristics of the signals. Which of the following is not a characteristic of these signals? ( )
A. Peak position
B. Peak splitting
C. Peak height
D. Height of the integration line

5. Which of the following statements regarding “nuclear spin relaxation” is incorrect? ( )
A. Without relaxation, nuclear magnetic resonance would not occur.
B. The width of the spectral lines is inversely proportional to the relaxation time.
C. Relaxation helps maintain a small majority of nuclei in their high-energy states.
D. Relaxation is divided into longitudinal and transverse relaxation.

II. Fill-in-the-blank questions (18 points in total)
1. How many different types of protons are present in each of the following compounds? What is the ratio of the peak areas corresponding to these protons in the proton NMR spectrum? (6 points) Compound, type of proton, ratio of corresponding peak areas: (CH3)2CHCH2CH(CH3)2, CH3COOH, CH3CH2CONH2. 2. Deduce the structural formulas from the following molecular formulas and 1H NMR data; a→b→c indicates the order from high field to low field. (12 points) Molecular formula, 1H NMR data, possible structural formulas: C9H10O2. Three sets of peaks: a: 3H, single peak ； b: 2H, single peak ； c: 5H, single peak; C9H12, three peaks; a: 6H, double peak ； b: 1H, septet ； c: 5H, single peak; C3H8O, three peaks; a: 6H, double peak ； b: 1H, single peak ； c: 1H, septet; C3H6BrCl, three peaks; a: 2H, multiplet ； b: 2H, three peaks ； c: 2H, triplet. III. In which regions of the infrared spectrum do the following compounds exhibit distinct absorption features? (3 points per question, total 6 points) (1) (C6H5)3CCHO? (2) CH3C≡CH. III. Determine the structure of the compounds. 1. A compound has the molecular formula C8H8; its infrared spectrum data are as follows. Determine its structural formula and indicate the origin of each absorption peak. (5 points) 2. IR (cm-1): 3050, 3060, 1640, 1600, 1500, 1420, 990, 910, 760, 710. 2. Another compound has the molecular formula C5H8O; its infrared spectrum shows peaks at 3020, 2900, 1690, and 1620 cm-1. Its UV absorption maximum is at 227 nm. It is not an aldehyde. Identify possible structures for this compound. (6 points) Mass spectrometry (total 10 points) I. Fill in the blanks (2 points). Using a low-resolution mass spectrometer, the mass-to-charge ratios of the following ions are: C3H7+, C8H19N+. II. A compound has the molecular formula C6H12O; its mass spectrometry data show that the m/e value of the M+ ion is 100. There are also fragment ion peaks at m/e 71, 57 (the base peak), 43, and 29. Attempt to deduce the structural formula of this compound and write out the cleavage process (8 points).