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CHM3122 IR probs Mon 22Nov

CHM3122 IR probs Mon 22Nov - IR Lecture 5(problem 8 O O...

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1 IR Lecture 5 (problem 8) ν (cm -1 ) assignment 3075, 3052 1771 1601 753, 699 sp 2 ν (C-H) -- no sp 3 ν (C-H)? ν (C=O) looks like ester (1750-1735) with C=O strengthened by conjugation on the "ether" end ν (C=C) for aromatic C-H, C=C oop bend; monosubstituted phenyl ν( C(O)O), ν( OCC) O O
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2 IR Lecture 5 (problem 9) ν (cm -1 ) assignment 3352, 3198 2820 1679 1617 ν (N-H) for 1 amine or amide ˚ sp 3 ν (C-H)? low, weak... overtone? ν (C=O) weakened by conjugation α to C=O: amide I band N-H bend: amide II band Note ν (C=C) is obscured solid sample O NH 2
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3 IR Lecture 5 problem 10 ν (cm -1 ) assignment 3036 2866-2936 1779 1748 884 sp 2 ν (C-H) sp 3 ν (C-H) ν (C=O) strengthened by inductive effect; halogen α to C=O? Mass spec would tell! Fermi resonance of C=O and 884 oop p-subst ring? high; strengthened... Cl O
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4 IR Lecture 5 problem 11 Molecular formula: C8H8O2 Assign the IR spectrum to one of the isomers shown: O O O O phenyl acetate methyl benzoate Reasoning: ν (CO) band at 1771 indicates strengthening of the C=O bond relative to the baseline ketone value of 1715: inductive effect of "ether" O reinforced by a-unsaturation (delocalization of O l.p onto ring?) For methyl benzoate, inductive effect is offset by conjugation 1771
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