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The substitution structure, barrier to internal rotation, and low frequency vibrations of pyruvic acid

Authors
Journal
Chemical Physics
0301-0104
Publisher
Elsevier
Publication Date
Volume
23
Issue
2
Identifiers
DOI: 10.1016/0301-0104(77)89002-2

Abstract

Abstract The microwave spectra of all singly and one multiply substituted species of pyruvic acid (CH 3COCOOH) have been measured, and the complete substitution structure has been calculated. The structure determined is as follows: O  H = 0.983 (5) A, C  O = 1.328 (5) Å, C = O carboxyl 1.215 (5) A, C = O keto, = 1.231 (5) A, C carboxyl  C keto = 1.523 (3) Å, C methyl  C keto = 1.486 (4) Å, CH in-plane = 1.074 (2) A, C  H out-of-plane = 1.106 (6) A, C  O  H = 105.2 (1.9)°, C  C  O hydroxyl = 114.5 (1.3)°, C  C  C = 118.6 (1.2)°, C  C = O keto = 117.0 (1.6)°, C  C = O carboxyl = 122.0 (1.8)°, C  C 0 H in-plane = 110.7 (1.1)°, C  C  H out-of-plane = 109.0 (2.6)°. From relative intensity measurements the lowest vibrational mode, the C  C torsion, has been found to lie at 101 ± 9 cm −1, whilst the next higher mode, the methyl torsion, lies at 134 ± 7 cm −1. The barrier to internal rotation of the methyl group has been determined, fustly, from the vibrational ground state spectrum alone ( V 3 = 339.4 ± 0.5 cm −1), and, secondly, from both the vibrational ground and methyl torsion first excited state spectra ( V 3 = 355 ± 5 cm −1, V 6 = −20 ± 10 cm −1).

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