Carbon–hydrogen bond

 ( Organic Chemistry ) 

In chemistry, the carbon–hydrogen bond ( bond) is a chemical bond between carbon and hydrogen atoms that can be found in many . This bond is a covalent bond, single bond, meaning that carbon shares its outer with up to four hydrogens. This Octet rule both of their Electron shell, making them stable.

Carbon–hydrogen bonds have a bond length of about 1.09 Å (1.09 × 10⁻¹⁰ m) and a bond energy of about 413 Joule/mol (see table below). Using Pauling's scale—C (2.55) and H (2.2)—the electronegativity difference between these two atoms is 0.35. Because of this small difference in electronegativities, the bond is generally regarded as being non-polar. In structural formulas of molecules, the hydrogen atoms are often omitted. Compound classes consisting solely of bonds and bonds are , , , and aromatic hydrocarbons. Collectively they are known as hydrocarbons.

In October 2016, astronomers reported that the very basic chemical ingredients of life—the carbon–hydrogen molecule (CH, or methylidyne radical), the carbon–hydrogen positive ion () and the carbon ion ()—are created, in large part, using energy from the ultraviolet light of nearby , rather than in other ways, such as turbulent events related to supernovae and , as thought earlier.

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Bond length The length of the carbonhydrogen bond varies slightly with the hybridisation of the carbon atom. A bond between a hydrogen atom and an sp² hybridised carbon atom is about 0.6% shorter than between hydrogen and sp³ hybridised carbon. A bond between hydrogen and sp hybridised carbon is shorter still, about 3% shorter than sp³ C–H. This trend is illustrated by the molecular geometry of ethane, ethylene and acetylene.

+Comparison of bond lengths in simple hydrocarbonsCRC Handbook of Chemistry and Physics, 88th edition

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Reactions The C−H bond in general is very strong, so it is relatively unreactive. In several compound classes, collectively called , the C−H bond can be sufficiently acidic for proton removal. Unactivated C−H bonds are found in alkanes and are not adjacent to a heteroatom (O, N, Si, etc.). Such bonds usually only participate in radical substitution. Many enzymes are known, however, to effect these reactions.Bollinger, J. M. Jr., Broderick, J. B. "Frontiers in enzymatic C-H-bond activation" Current Opinion in Chemical Biology 2009, vol. 13, page 51-7.

Although the C−H bond is one of the strongest, it varies over 30% in magnitude for fairly stable organic compounds, even in the absence of heteroatoms.Yu-Ran Luo and Jin-Pei Cheng "Bond Dissociation Energies" in CRC Handbook of Chemistry and Physics, 96th Edition

CH3−H	Methyl	104	440
C2H5−H	Ethyl group	98	410
(CH3)2HC−H	Isopropyl	95	400
(CH3)3C−H	tert-Butyl	93	390
CH2=CH−H	vinyl group	112	470
HC≡C−H	ethynyl	133	560
C6H5−H	phenyl	110	460
CH2=CHCH2−H	Allyl	88	370
C6H5CH2−H	Benzyl	85	360
OC4H7−H	THF	92	380
CH3C(O)CH2−H	acetone	96	400

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See also

• Carbon–carbon bond
• Carbon–nitrogen bond
• Carbon–oxygen bond
• Carbon–fluorine bond

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