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Material Type: Exam; Professor: Bisht; Class: Organic Chemistry II; Subject: Chemistry; University: University of South Florida; Term: Summer 2008;
Typology: Exams
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1) Which compound would be expected to show intense IR absorption at 3000-3100 cm-1? A) CH3C≡CCH
B) butane C) but-1-ene D) CH3CH2C≡CH
2) Which compound would show a larger than usual M+2 peak in the mass spectrum? A) (CH3)2CHNH
B) CH3CHBrCH
C) CH3CH2CO2H
D) CH3(CH2)2CH
3) Which has a lower characteristic IR stretching frequency, the C–H or C–D bond? Explain briefly. Answer: C–D; heavier atoms vibrate more slowly
4) What effect does conjugation typically have on the frequency at which IR absorption by C=C occurs? A) Conjugation does not affect the frequency at which absorption occurs. B) Conjugation increases the frequency at which absorption occurs. C) Conjugation decreases the frequency at which absorption occurs.
Answer: C=C stretch around 1640 cm-1; vinylic C-H stretch above 3000 cm-1 for first compound. C=O stretch is around 1700 cm-1 and no vinylic stretch for second compound
6) The frequency of the stretching vibration of a bond in IR spectroscopy depends on what two quantities? A) the stiffness of the bond and the electronegativity of the atoms B) the electronegativity of the atoms and the nuclear charges of the atoms C) the masses of the atoms and the strength of the bond D) the nuclear charges of the atoms and the atomic radii E) the electronegativity of the atoms and the masses of the atoms
7) Rank the following bonds in order of increasing stretching frequency (cm-1) in IR spectroscopy: C=C, C≡C, C–O, and C=O.
1a 2a 3a 4a 5a 6a 7a 0
8) Which compound would be expected to show intense IR absorption at 2250 cm-1? A) CH3CH2CH2CO2H
B) (CH3)2CHCH2OH
C) (CH3)2CHCN
D) CH3CH2CH2CONH
9) Which of the following structures is consistent with the IR spectra shown below?
10) The protons marked Ha and Hb in the molecule below are ____B______.
A) enantiotopic B) chemically equivalent C) diastereotopic D) none of the above
11) The protons marked Ha in the molecule below will be a __ triplet ________ (indicate the splitting here).
12) Predict the number of signals in the 13C NMR spectrum of the two cyclohexanes shown below.
__ 3 ____ signals ___7_____ signals
13) Predict the number of signals expected (disregarding splitting) in the 1H spectrum of 2-methoxybutane.