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EXAM 1 CHEMISTRY 2211 July 14th 2008
NAME (Please Print)_________________________________
TA’s Name…………….…………………………………SEC #……………….
Q. 1- 15- (2.5 points each)
1) Which compound would be expected to show intense IR absorption at 3000-3100 cm-1?
A) CH3C≡CCH3
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)2CHNH2
B) CH3CHBrCH3
C) CH3CH2CO2H
D) CH3(CH2)2CH3
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.
5) How could IR spectroscopy be used to distinguish between the following pair of compounds?
CH2=CHCH2CH(CH3)2 and CH3COCH2CH(CH3)2
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.
Answer: C–O < C=C < C=O < C≡C
HHe
Li Be BCNOFNe
Na Mg Al Si PSCl
Ar
1a 2a 3a 4a 5a 6a 7a 0
