Double bond


Double bond

A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in a carbonyl group with a carbon atom and an oxygen atom. Other common double bonds are found in azo compounds (N=N), imines (C=N) and sulfoxides (S=O). In skeletal formula the double bond is drawn as two parallel lines (=) between the two connected atoms; typographically, the equals sign is used for this.[1][2]

Double bonds are stronger than single bonds and double bonds are also shorter. The bond order is two. Double bonds are also electron-rich, which makes them reactive.

Ethylene-CRC-MW-dimensions-2D.png
Acetone-CRC-MW-ED-dimensions-2D.png
DMSO-2D-dimensions.png
ethylene acetone dimethyl sulfoxide
Common chemical compounds with double bonds

Contents

Bonding

The type of bonding can be explained in terms of orbital hybridization. In ethylene each carbon atom has three sp2 orbitals and one p-orbital. The three sp2 orbitals lie in a plane with 120° angles. The p-orbital is perpendicular to this plane. When the carbon atoms approach each other, two of the sp2 orbitals overlap to form a sigma bond. At the same time, the two p-orbitals approach (again in the same plane) and together they form a pi-bond. For maximum overlap, the p-orbitals have to remain parallel, and, therefore, rotation around the central bond is not possible. This property gives rise to cis-trans isomerism. Double bonds are shorter than single bonds because p-orbital overlap is maximized.

Double bond presentation Double bond presentation
2 sp2 orbitals (total of 3 such orbitals) approach to form a sp2-sp2 sigma bond Two p-orbitals overlap to form a pi-bond in a plane parallel to the sigma plane


With 133 pm, the C−C bond length is shorter than the C−C length in ethane with 154 pm. The double bond is also stronger, 636 (KJ/mol) versus 368 kJ/mole but not twice as much as the pi-bond is weaker than the sigma bond due to less effective pi-overlap.

In an alternative representation, the double bond results from two overlapping sp3 orbitals as in a bent bond.[3]

Types of double bonds between atoms

C O N S
C alkene carbonyl group imine thioketone, thial
O dioxygen nitroso compound sulfoxide, sulfone, sulfinic acid, sulfonic acid
N azo compound
S disulfur

Variations

In molecules with alternating double bonds and single bonds, p-orbital overlap can exist over multiple atoms in a chain, giving rise to a conjugated system. Conjugation can be found in systems such as dienes and enones. In cyclic molecules, conjugation can lead to aromaticity. In cumulenes two double bonds are adjacent.

Double bonds are common for period 2 elements carbon, nitrogen, and oxygen, and less common with elements of higher periods. Metals, too, can engage in multiple bonding in a metal ligand multiple bond.

References

  1. ^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7 
  2. ^ Organic Chemistry 2nd Ed. John McMurry
  3. ^ Advanced Organic Chemistry Carey, Francis A., Sundberg, Richard J. 5th ed. 2007

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Look at other dictionaries:

  • double bond — Bond Bond (b[o^]nd), n. [The same word as band. Cf. {Band}, {Bend}.] 1. That which binds, ties, fastens, or confines, or by which anything is fastened or bound, as a cord, chain, etc.; a band; a ligament; a shackle or a manacle. [1913 Webster]… …   The Collaborative International Dictionary of English

  • double bond — n a chemical bond in which two pairs of electrons are shared by two atoms in a molecule and which is usu. represented in chemical formulas by two lines (as in the formula for ethylene H2C=CH2) compare TRIPLE BOND see UNSATURATED (b) …   Medical dictionary

  • double bond — n. Chem. the sharing of two pairs of electrons between two atoms, usually represented in structural formulas by dots or dashes, as C:C or C=C …   English World dictionary

  • double bond — UK / US noun [countable] Word forms double bond : singular double bond plural double bonds chemistry a chemical bond in which two atoms share two pairs of electrons …   English dictionary

  • double bond — dvigubasis ryšys statusas T sritis chemija apibrėžtis Du kovalentiniai ryšiai tarp dviejų atomų. atitikmenys: angl. double bond; ethylene bond rus. двойная связь; этиленовая связь ryšiai: sinonimas – dvilypis ryšys sinonimas – etileninis ryšys …   Chemijos terminų aiškinamasis žodynas

  • double bond — dvilypis ryšys statusas T sritis fizika atitikmenys: angl. double bond vok. Doppelbindung, f rus. двойная связь, f pranc. liaison double, f …   Fizikos terminų žodynas

  • double bond — noun a covalent bond in which two pairs of electrons are shared between two atoms • Hypernyms: ↑covalent bond * * * noun, pl ⋯ bonds [count] technical : a chemical bond in which two atoms in a molecule share two pairs of electrons compare ↑single …   Useful english dictionary

  • double bond — noun Date: 1889 a chemical bond in which two pairs of electrons are shared by two atoms in a molecule compare single bond, triple bond …   New Collegiate Dictionary

  • double bond — A bond providing a penalty for its nonfulfillment, as distinguished from a single bond which carries no penalty …   Ballentine's law dictionary

  • double bond — noun A covalent bond in which two electron pairs (instead of the usual one) are shared between two atoms; most common between carbon atoms and carbon, oxygen or nitrogen atoms, but several other forms are known …   Wiktionary


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