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A multiple covalent bond is a chemical bond in which two atoms share more than one pair of electrons . The name is used to distinguish these types of covalent bonds from simple bonds, in which a single pair of electrons is shared.
The most common examples of multiple bonds are double bonds and triple bonds . These types of bonds appear frequently in many organic and inorganic compounds.
In general terms, multiple bonds are characterized by being stronger (their bond energies are higher) and shorter than single bonds between the same two elements.
the double bond
The double bond is the first of the multiple bonds. It is easily recognized as it is represented by a pair of parallel lines between the two bonded atoms. This type of bond is formed between two atoms that have sp 2 hybridization (as in the case of alkenes), one sp 2 and the other sp (as in the case of allenes and carbon dioxide), or between two sp hybridized atoms (as in the case of cumulenes).
They are called double bonds since they are made up of two bonds:
- A σ (Greek letter sigma) bond.
- A π bond (Greek letter pi).
The σ bond is formed by the frontal overlap between hybrid atomic orbitals (sp or sp 2 , for example). On the other hand, the π bond is formed by the lateral overlap of pure (unhybridized) atomic orbitals such as po orbitals, in some cases some d orbitals.
The electrons that are part of the sigma bond can be found, most of the time, in the space between the two nuclei of the bonded atoms. The electrons in the π bond are found in lobes on either side of a plane that divides the molecule through the bond, as shown in the following figure.
An important characteristic of double bonds is that they are rigid bonds, which means that they do not allow rotation along the bond. They are also stronger and shorter than single links.
Examples of compounds with double bonds
A wide variety of organic compounds have double bonds (also called double bonds):
- Alkenes have carbon-carbon double bonds (C=C)
- Aldehydes, ketones, carboxylic acids, esters, amides, imides, and anhydrides all contain, as part of their structure, one or more carbonyl groups, which consist of a carbon atom linked to oxygen by a double bond.
- Imines have C=N double bonds.
- As mentioned before, allenes and cumulenes have multiple consecutive C=C double bonds.
the triple bond
A triple bond is a multiple covalent bond made up of 3 bonding pairs of electrons. It is easily recognized as it is represented by three parallel lines between the two atoms it joins (C≡C, for example).
This type of multiple covalent bond is formed between atoms that possess sp hybridization. They are called triple bonds since they are made up of three bonds:
- a σ bond.
- Two π bonds.
In this case, the σ bond is formed by the frontal overlap between sp-sp hybrid atomic orbitals, while each π bond is formed by the sideways overlap of two pairs of parallel p pure atomic orbitals.
The sigma bond of the triple bond is similar to that of the double bond, but the two π bonds merge into a single, roughly tubular-shaped region with the bonded atoms in the center, as shown in the figure below.
Compared to double bonds, triple bonds are stronger and they are also shorter.
Examples of compounds with triple bonds
The triple bond is an electron-rich bond found in the following organic functional groups and inorganic molecules:
- Alkynes have carbon-carbon triple bonds (C≡C)
- The nitrogen molecule (N 2 ) and the carbon monoxide molecule have, respectively, triple bonds :N ≡N: and – :C≡O: +
- Nitriles possess triple bonds -C ≡ N:
- Inorganic cyanide salts and hydrocyanic acid also contain the same bond – :C ≡N:
- Other heavier elements such as tungsten also form triple bonds, as in the case of hexa(tert-butoxy)ditungsten(III)
References
Carey, F. (1999). Organic Chemistry (3rd ed.). Madrid, Spain: McGraw-Hill Companies.
Libretexts. (2021, March 20). 3.2.2: Multiple Bonds. Retrieved from https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Map%3A_Inorganic_Chemistry_(Miessler_Fischer_Tarr)/03%3A_Simple_Bonding_Theory/3.02%3A_Valence_Shell_Electron-Pair_Repulsion/3.2.02%3A_Multiple_Bond yes
multiple links. (2020, October 30). Retrieved from https://espanol.libretexts.org/@go/page/1864
March, Jerry (1985). Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.). New York: Wiley. ISBN 0-471-85472-7.
