The C−H bond is a bond between carbon and hydrogen atoms, most commonly found in 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 (2.5) and H (2.1)—the electronegativity difference between these two atoms is 0.4. 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.
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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.
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.[2]
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 |
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 | Uuq | Uup | Uuh | Uus | Uuo | |
↓ | |||||||||||||||||
CLa | CCe | CPr | CNd | CPm | CSm | CEu | CGd | CTb | CDy | CHo | CEr | CTm | CYb | CLu | |||
Ac | Th | Pa | CU | Np | Pu | Am | Cm | Bk | Cf | Es | Fm | Md | No | Lr |
Core organic chemistry | Many uses in chemistry |
Academic research, but no widespread use | Bond unknown / not assessed |