Carbon–hydrogen Bond - Wikipedia

Covalent chemical bond between hydrogen and carbon atoms

In chemistry, the carbon–hydrogen bond (C−H bond) is a chemical bond between carbon and hydrogen atoms that can be found in many organic compounds.[1] This bond is a covalent, single bond, meaning that carbon shares its outer valence electrons with up to four hydrogens. This completes both of their outer shells, making them stable.[2]

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.

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 (CH+) and the carbon ion (C+)—are created, in large part, using energy from the ultraviolet light of nearby stars, rather than in other ways, such as turbulent events related to supernovae and young stars, as thought earlier.[3]

Bond length

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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.[citation needed]

Comparison of bond lengths in simple hydrocarbons[4]

Molecule	Methane	Ethane	Ethylene	Acetylene
Formula	CH4	C2H6	C2H4	C2H2
Class	alkane	alkane	alkene	alkyne
Structure
Hybridisation of carbon	sp3	sp3	sp2	sp
C–H bond length	1.087 Å	1.094 Å	1.087 Å	1.060 Å
Proportion of ethane C–H bond length	99%	100%	99%	97%
Structure determination method	microwave spectroscopy	microwave spectroscopy	microwave spectroscopy	infrared spectroscopy

Reactions

[edit] Main article: Carbon–hydrogen bond activation

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 effect these reactions.[5]

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.[6][7]

Bond	Hydrocarbon radical	Molar Bond Dissociation Energy (kcal)	Molar Bond Dissociation Energy (kJ)
CH3−H	Methyl	104	440
C2H5−H	Ethyl	98	410
(CH3)2HC−H	Isopropyl	95	400
(CH3)3C−H	tert-Butyl	93	390
CH2=CH−H	vinyl	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	tetrahydrofuranyl	92	380
CH3C(O)CH2−H	acetonyl	96	400

See also

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

References

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1. ^ March, Jerry (1985). Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.). New York: Wiley. ISBN 9780471854722. OCLC 642506595.
2. ^ "Life Sciences Cyberbridge". Covalent Bonds. Archived from the original on 2015-09-18. Retrieved 2015-09-15.
3. ^ Landau, Elizabeth (12 October 2016). "Building Blocks of Life's Building Blocks Come From Starlight". NASA. Retrieved 13 October 2016.
4. ^ CRC Handbook of Chemistry and Physics, 88th edition
5. ^ 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. doi:10.1016/j.cbpa.2009.03.018
6. ^ "Bond Energies". Organic Chemistry, Michigan State University. Archived from the original on 29 August 2016.
7. ^ Yu-Ran Luo and Jin-Pei Cheng "Bond Dissociation Energies" in CRC Handbook of Chemistry and Physics, 96th Edition

v t e Molecules detected in outer space
Molecules	Diatomic Aluminium monochloride Aluminium monofluoride Aluminium(II) oxide Argonium Carbon cation Carbon monophosphide Carbon monosulfide Carbon monoxide Cyano radical Diatomic carbon Fluoromethylidynium Helium hydride ion Hydrogen chloride Hydrogen fluoride Hydrogen (molecular) Hydroxyl radical Imidogen Iron(II) oxide Magnesium monohydride Methylidyne radical Nitric oxide Nitrogen (molecular) Oxygen (molecular) Phosphorus monoxide Phosphorus mononitride Potassium chloride Silicon carbide Silicon monoxide Silicon monosulfide Sodium chloride Sodium iodide Sulfanyl Sulfur mononitride Sulfur monoxide Titanium(II) oxide Triatomic Aluminium(I) hydroxide Aluminium isocyanide Amino radical Carbon dioxide Carbonyl sulfide CCP radical Chloronium Diazenylium Dicarbon monoxide Disilicon carbide Ethynyl radical Formyl radical Hydrogen cyanide (HCN) Hydrogen isocyanide (HNC) Hydrogen sulfide Hydroperoxyl Iron cyanide Isoformyl Magnesium cyanide Magnesium isocyanide Methylene Methylidynephosphane N2H+ Nitrous oxide Nitroxyl Ozone Potassium cyanide Sodium cyanide Sodium hydroxide Silicon carbonitride c-Silicon dicarbide SiNC Sulfur dioxide Thioformyl Thioxoethenylidene Titanium dioxide Tricarbon Trihydrogen cation Water Fouratoms Acetylene Ammonia Cyanoethynyl Formaldehyde Fulminic acid HCCN Hydrogen peroxide Hydromagnesium isocyanide Isocyanic acid Isothiocyanic acid Ketenyl Methyl cation Methyl radical Methylene amidogen Propynylidyne Protonated carbon dioxide Protonated hydrogen cyanide Silicon tricarbide Thiocyanic acid Thioformaldehyde Tricarbon monosulfide Tricarbon monoxide Fiveatoms Ammonium ion Butadiynyl Carbodiimide Cyanamide Cyanoacetylene Cyanoformaldehyde Cyanomethyl Cyclopropenylidene Formic acid Isocyanoacetylene Ketene Methane Methoxy radical Methylenimine Propadienylidene Protonated formaldehyde Silane Silicon-carbide cluster Sixatoms Acetonitrile Cyanobutadiynyl radical Cyclopropenone Diacetylene E-Cyanomethanimine Ethylene Formamide HC4N Ketenimine Methanethiol Methanol Methyl isocyanide Pentynylidyne Propynal Protonated cyanoacetylene Sevenatoms Acetaldehyde Acrylonitrile Vinyl cyanide Cyanodiacetylene Ethylene oxide Glycolonitrile Hexatriynyl radical Methyl isocyanate Methylamine Propyne Vinyl alcohol Eightatoms Acetic acid Acrolein Aminoacetonitrile Cyanoallene Ethanimine Glycolaldehyde Hexapentaenylidene Methyl formate Methylcyanoacetylene Nineatoms Acetamide Cyanohexatriyne Dimethyl ether Ethanethiol Ethanol Methyldiacetylene N-Methylformamide Octatetraynyl radical Propene Propionitrile Tenatomsor more Acetone Benzene Benzonitrile Buckminsterfullerene (C60, C60+, fullerene, buckyball) Butyronitrile C70 fullerene Cyanodecapentayne Ethyl formate Ethylene glycol Heptatrienyl radical Methyl acetate Methyl-cyano-diacetylene Methyltriacetylene Propionaldehyde Pyrimidine
Deuteratedmolecules	Ammonia Ammonium ion Formaldehyde Formyl radical Heavy water Hydrogen cyanide Hydrogen deuteride Hydrogen isocyanide N2D+ Propyne Trihydrogen cation
Unconfirmed	Anthracene Dihydroxyacetone Glycine Graphene H2NCO+ Hemolithin Linear C5 Methoxyethane Naphthalene cation Phosphine Pyrene Silylidyne
Related	Abiogenesis Astrobiology Astrochemistry Atomic and molecular astrophysics Chemical formula Circumstellar dust Circumstellar envelope Cosmic dust Cosmic ray Cosmochemistry Diffuse interstellar band Earliest known life forms Extraterrestrial life Extraterrestrial liquid water Forbidden mechanism Homochirality Intergalactic dust Interplanetary medium Interstellar medium Iron–sulfur world theory Kerogen Molecules in stars Nexus for Exoplanet System Science Organic compound Outer space PAH world hypothesis Photodissociation region Polycyclic aromatic hydrocarbon (PAH) Pseudo-panspermia RNA world hypothesis Spectroscopy Tholin
Category:Astrochemistry Outer space portal Astronomy portal Chemistry portal

v t e Compounds of carbon with other elements in the periodic table
CH CHe CLi CBe CB CC CN CO CF CNe 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 CLu CHf CTa CW CRe COs CIr CPt CAu CHg CTl CPb CBi CPo CAt Rn Fr CRa Lr Rf Db CSg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og   CLa CCe CPr CNd CPm CSm CEu CGd CTb CDy CHo CEr CTm CYb Ac CTh CPa CU CNp CPu CAm CCm CBk CCf CEs Fm Md No
Legend	Chemical bonds to carbon Core organic chemistry Many uses in chemistry Academic research, no widespread use Bond unknown