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George P , Glusker JP , Bock CW
Bond Angles around Tetrahedrally Bonded Carbon, and Distortion of the Tetrahedron in Ch3-X Structures
Theochem-Journal of Molecular Structure. 1995 Aug 28;338 :155-173
PMID: ISI:A1995RR60800015   
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Abstract
To investigate the extent to which individual bond angles around a tetrahedrally bonded carbon atom deviate from the regular tetrahedral angle of 109.47 degrees, and the sum of the six angles from the maximum value of 656.83 degrees, we have used results derived from neutron diffraction studies on molecules containing the X-CH2-Y grouping, and corresponding results for CH3-X, X-CH2-Y and H-CXYZ structures calculated using ab initio molecular orbital methods. In both sets of data the individual values vary between 105 degrees and 117 degrees. Yet, provided there is no steric constraint such as the bonding of the carbon in a four- or three-membered ring, the summation of the angles is less than the maximum by only a few tenths of a degree, An inherent tendency for the summation to attain this maximum value is further substantiated by the data for CCC and COC rings. Even though the CCC and CCO ring angles are about 60 degrees, compensatory increases in the remaining five angles are sufficiently large to reduce the deficit in the summation to approximately 14 degrees. The distorsion of the tetrahedra is discussed in terms of the interplay between bond angle relationships and the bond lengths. In the CH3-X structures in which C-X is a trigonal axis of symmetry, the tetrahedra are elongated along this axis. In other CH3-X structures, where two of the hydrogen atoms, H-b and H-c, are located symmetrically about the plane containing C, X, and the other hydrogen atom, H-a, the tetrahedra are also elongated but tilted a little toward, or away from, the H-b-H-c side of the HaHbHc triangle at the base of the tetrahedron.
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Times Cited: 1 Article RR608 THEOCHEM-J MOL STRUCT