Reviewquestions_12

Reviewquestions_12
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Unformatted text preview: 1 1) Which compound would be expected to show intense IR absorption at 3300 cm-1 ? A) CH 3 C ≡ CCH 3 B) butane C) but-1-ene D) CH 3 CH 2 C ≡ CH Answer: D 2) Which compound would be expected to show intense IR absorption at 2820, 2710 and 1705 cm-1 ? A) CH 3 COCH 2 CH 3 B) PhCOCH 3 C) PhCHO D) CH 2 =CHCOCH 3 Answer: C 3) Which compound would be expected to show intense IR absorption at 2250 cm-1 ? A) CH 3 CH 2 CH 2 CO 2 H B) (CH 3 ) 2 CHCH 2 OH C) (CH 3 ) 2 CHCN D) CH 3 CH 2 CH 2 CONH 2 Answer: C 4) Which compound would be expected to show intense IR absorption at 1680 cm-1 ? Answer: Compound C 5) Deduce a possible structure for the compound with the IR absorptions below. C 3 H 3 Br: 3300, 2900, 2100 cm-1 Answer: HC ≡ CCH 2 Br 6) Deduce a possible structure for the compound with the IR absorptions below. C 3 H 5 N: 2950, 2250 cm-1 Answer: CH 3 CH 2 CN 2 7) Deduce a possible structure for the compound with the IR absorptions below. C 5 H 8 O: 2950, 1750 cm-1 Answer: cyclopentanone 8) Deduce a possible structure for the compound with the IR absorptions below. C 4 H 8 O: 2950, 2820, 2715, 1715 cm-1 Answer: CH 3 CH 2 CH 2 CHO 9) Deduce a possible structure for the compound with the IR absorptions below. C 6 H 10 : 3040, 2980, 1660 cm-1 Answer: cyclohexene 10) How could IR spectroscopy be used to distinguish between the following pair of compounds? CH 3 OCH 2 CH 3 and CH 3 CH 2 CH 2 OH Answer: O-H stretch at 3300 cm-1 11) How could IR spectroscopy be used to distinguish between the following pair of compounds? HOCH 2 CH 2 CHO and CH 3 CH 2 CO 2 H Answer: A carboxylic acid will have a very broad O–H absorption near 3000 cm-1 ; an aldehyde has characteristic C–H stretches at 2820 and 2720 cm-1 . 12) How could IR spectroscopy be used to distinguish between the following pair of compounds? CH 3 COCH=CHCH 2 CH 3 and CH 3 COCH 2 CH 2 CH=CH 2 Answer: C=O absorption in conjugated carbonyl appears at lower wavenumber 13) How could IR spectroscopy be used to distinguish between the following pair of compounds? CH 3 CH 2 C ≡ CH and CH 3 C ≡ CCH 3 Answer: Terminal alkyne stretch at 3300 cm-1 , lower intensity C ≡ C absorption in internal alkyne 14) Ethyne (HC ≡ CH) does not show IR absorption in the region 2000-2500 cm-1 because: A) C–H stretches occur at lower energies. B) C ≡ C stretches occur at about 1640 cm-1 . C) there is no change in the dipole moment when the C ≡ C bond in ethyne stretches. D) there is a change in the dipole moment when the C ≡ C bond in ethyne stretches. Answer: C 3 15) Describe the molecular ion region in the mass spectrum of CH 3 CH 2 Br. Answer: The natural abundance of the isotopes 79 Br and 81 Br are about the same; therefore, there will be peaks of equal intensity at m/z 108 and 110. ...
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