In
chemistry, the carbon-hydrogen bond ( bond) is a
chemical bond
A chemical bond is a lasting attraction between atoms or ions that enables the formation of molecules and crystals. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds, or through the sharing o ...
between
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
and
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
atoms that can be found in many
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s.
This bond is a
covalent,
single bond, meaning that carbon shares its outer
valence electron
In chemistry and physics, a valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed. In a single covalent bond, a shared pair f ...
s with up to four hydrogens. This
completes both of their
outer shells, 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
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 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
alkane
In organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms tha ...
s,
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s,
alkynes, and
aromatic hydrocarbons. Collectively they are known as
hydrocarbons
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
.
In October 2016, astronomers reported that the very basic chemical ingredients of
life
Life is a quality that distinguishes matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes, from that which does not, and is defined by the capacity for Cell growth, growth, reaction to Stimu ...
—the carbon-hydrogen molecule (CH, or
methylidyne radical), the carbon-hydrogen positive ion () and the carbon ion ()—are the result, in large part, of
ultraviolet light from
star
A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...
s, rather than in other ways, such as the result of turbulent events related to
supernovae and
young stars, as thought earlier.
Bond length
The length of the carbon-hydrogen bond varies slightly with the
hybridisation of the carbon atom. A bond between a hydrogen atom and an sp
2 hybridised carbon atom is about 0.6% shorter than between hydrogen and sp
3 hybridised carbon. A bond between hydrogen and sp hybridised carbon is shorter still, about 3% shorter than sp
3 C-H. This trend is illustrated by the
molecular geometry
Molecular geometry is the three-dimensional space, three-dimensional arrangement of the atoms that constitute a molecule. It includes the general shape of the molecule as well as bond lengths, bond angles, torsional angles and any other geometric ...
of ethane, ethylene and acetylene.
Reactions
The C−H bond in general is very strong, so it is relatively 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. Many enzymes are known, however, to affect these reactions.
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
]
See also
*
Carbon–carbon bond
*
Carbon–nitrogen bond
*
Carbon–oxygen bond
*
Carbon–fluorine bond
References
{{DEFAULTSORT:Carbon-hydrogen bond
Organic chemistry
Chemical bonding