Sp³-гібридизований Карбон

Hybridisation

Hybrid orbitals are useful in the explanation of molecular geometry and atomic bonding properties. Each hybrid is denoted sp3 to indicate its composition, and in methane each is directed along one of the four C-H bonds. Hybridisation theory is an integral part of organic chemistry.

Geometry

In methane, four sp3 hybrid orbitals overlap the 1s orbitals of the four hydrogens, giving four sigma bonds of equal length and strength. Methane is a tetrahedral molecule with four equivalent C-H bonds. Sp3 hybridisation gives a tetrahedral shape with 109.5° angles, as in CCl4, whereas sp2 hybridisation gives a trigonal planar shape with 120° angles, as in BCl3.

The tetrahedral angle of about 109.47° is exact for methane, while larger alkanes generally have bonds within several degrees of this idealized value. In highly branched alkanes, the bond angle may differ from the optimal value (109.5°) to accommodate bulky groups.

Saturated hydrocarbons

An alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carbon-carbon bonds are single. In an alkane, each carbon atom is sp3-hybridized with 4 sigma bonds, either C-C or C-H. The C-H bond results from the overlap of an sp3 orbital of carbon with the 1s orbital of a hydrogen, and the C-C bond from the overlap of two sp3 orbitals on adjacent carbon atoms. The bond lengths are 1.09 × 10⁻¹⁰ m for a C-H bond and 1.54 × 10⁻¹⁰ m for a C-C bond.

In ethane, there is nearly free rotation about a carbon-carbon single bond. The staggered conformation of ethane is 12.6 kJ/mol lower in energy than the eclipsed conformation.

Aromatic and homoaromatic systems

An aromatic compound has a coplanar structure, with all of the contributing atoms in the same plane. In homoaromaticity, conjugation is interrupted by a single sp3 hybridized carbon atom.

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