Carbon–hydrogen bond

The carbon-hydrogen bond (C-H bond) is a bond between carbon and hydrogen atoms that can be found in many organic compounds.¹ Carbon–hydrogen bonds have a bond length of about 1.09 Å (1.09 × 10⁻¹⁰ m) and a bond energy of about 413 kJ/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 C−H bond is generally regarded as being non-polar. In structural formulas of molecules, the hydrogen atoms are often omitted. Compound classes consisting solely of C-H bonds and C-C bonds are alkanes, alkenes, alkynes, and aromatic hydrocarbons. Collectively they are known as hydrocarbons.

Reactions

The C−H bond in general is unreactive. In several compound classes, collectively called carbon acids, 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. Another reaction type involving C−H bonds is so-called C−H bond activation mediated by metals and carbene C−H insertion. C-H bond oxidation suffers from lack of selectivity. Enzymes are known for selective oxidations and some organic procedures exist ²

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.³

Bond	Hydrocarbon radical	Bond Dissociation Energy (kcal/mole)
CH₃−H	Methyl	103
C₂H₅−H	Ethyl	98
(CH₃)₂HC−H	Isopropyl	95
(CH₃)₃C−H	tert-Butyl	93
CH₂=CH−H	vinyl	112
C₆H₅−H	phenyl	110
CH₂=CHCH₂−H	Allyl	88
C₆H₅CH₂−H	Benzyl	85
OC₄H₇−H	tetrahydrofuranyl	92

Nomenclature

The C−H unit is formally named carbogen.

CH																	He
CLi	CBe											CB	CC	CN	CO	CF	Ne
CNa	CMg											CAl	CSi	CP	CS	CCl	CAr
CK	CCa	CSc	CTi	CV	CCr	CMn	CFe	CCo	CNi	CCu	CZn	CGa	CGe	CAs	CSe	CBr	CKr
CRb	CSr	CY	CZr	CNb	CMo	CTc	CRu	CRh	CPd	CAg	CCd	CIn	CSn	CSb	CTe	CI	CXe
CCs	CBa		CHf	CTa	CW	CRe	COs	CIr	CPt	CAu	CHg	CTl	CPb	CBi	CPo	CAt	Rn
Fr	Ra		Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Uut	Fl	Uup	Lv	Uus	Uuo
		↓
		CLa	CCe	CPr	CNd	Pm	CSm	CEu	CGd	CTb	CDy	CHo	CEr	CTm	CYb	CLu
		Ac	CTh	CPa	CU	CNp	CPu	CAm	CCm	CBk	Cf	CEs	Fm	Md	No	Lr

**Chemical bonds to carbon**
Core organic chemistry	Many uses in chemistry
Academic research, but no widespread use	Bond unknown

References

^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7
^ Adding Aliphatic C–H Bond Oxidations to Synthesis M. Christina White Science 17 February 2012: Vol. 335 no. 6070 pp. 807-809 doi:10.1126/science.1207661
^ http://www.cem.msu.edu/~reusch/OrgPage/bndenrgy.htm#dissbe

[March-1] March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7

[2] Adding Aliphatic C–H Bond Oxidations to Synthesis M. Christina White Science 17 February 2012: Vol. 335 no. 6070 pp. 807-809 doi:10.1126/science.1207661

[3] ttp://www.cem.msu.edu/~reusch/OrgPage/bndenrgy.htm#dissbe

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