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Title
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Conformational stability, structural parameters, barriers to internal rotation and vibrational assignment of cyclobutylamine
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Author
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Abstract
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| The infrared spectra (3600100 cm−1) of gaseous and solid cyclobutylamine, c-C4H7NH2 have been recorded, as well as, the infrared (360060 cm−1) spectra in xenon or krypton solutions at variable temperatures. From the latter studies, the enthalpy differences have been determined to be 225 ± 26 cm−1 (2.69 ± 0.31 kJ/mol) between the most stable equatorial-gauche (Eq-g) conformer and the equatorial-trans (Eq-t) form and 417 ± 42 cm−1 (4.99 ± 0.50 kJ/mol) with the axial-trans (Ax-t) conformer. At ambient temperature there is only 13 ± 1% of the Eq-t form present and 5 ± 1% of the Ax-t form. The potential function governing the conformational interchange of the NH2 moiety of the equatorial conformer has been determined with the following potential coefficients (cm−1): V1 = −176 ± 20, V2 = −199 ± 25, V3 = 721 ± 5 and V4 = 65 ± 10 with barriers of 784 cm−1 for gauche to gauche and 834 cm−1 for gauche to trans form. By utilizing previously reported microwave rotational constants for the Eq-g conformer along with the ab initio predicted structural parameters from the MP2(full)/6-311 + G(d,p) calculations, r0 structural parameters have been obtained for this conformer. The determined r0 heavy atom distances in Å are: (C1N) = 1.453(5); (C1C4) = 1.560(5); (C1C5) = 1.547(5); (C4C6) = 1.557(5); (C5C6) = 1.555(5) and the angles in degrees NC1C4 = 122.8(5)°; NC1C5 = 116.8(5)° with the four CCC ranging from 87.5° to 88.1°. A complete vibrational assignment is proposed for the (Eq-g) conformer based on the infrared band contours, infrared intensities, Raman activities and group frequencies which is supported by normal coordinate calculations utilizing the force constants from ab initio MP2(full)/6-31G(d) calculations. Proposed assignments are also made for several fundamentals of the (Eq-t) form and a few for the Ax-t conformer. The results are discussed and compared to the corresponding properties of some similar molecules. |
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Language
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English
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Source (journal)
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Journal of molecular structure. - Amsterdam
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Publication
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Amsterdam
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2009
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ISSN
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0022-2860
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DOI
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10.1016/J.MOLSTRUC.2008.07.013
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Volume/pages
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918
:1/3
(2009)
, p. 64-76
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ISI
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000263426100008
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Full text (Publisher's DOI)
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