Triple Bond Examples


The concept of chemical bonding in chemistry allows us to understand several behavioral aspects of the matter present around us. In the most fundamental terms, chemical bonding is nothing but the model representation of the interplay of forces that exist among atoms, just like the musical notes represent music on a page. Chemists use these models to understand interatomic/molecular interactions and their corresponding effects in the real world. Although all atoms are ordinarily electrically neutral, they are still unstable because of their empty valance shells. To gain stability, atoms share and donate/accept electrons from other atoms, thereby developing covalent and ionic bonds among them, respectively. When two atoms share three pairs (six electrons) among their valance shells, we say that a triple bond exists among them. The triple bond is represented on paper by something called Lewis Dot Structure with three straight lines (≡) drawn between the symbols of the corresponding chemical elements. Theoretical and experimental findings show that the bond length in the case of triple bonds is shorter than the equivalent single and double bonds. Consequently, triple bonds have more strength than single or double bonds, i.e., it would take more energy to break the triple bond in {N}_{2} compared to the double bond in {O}_{2}. It is important to note that multiple bonds (double and triple bonds) only occur among the atoms with the need to gain or lose at least two valence electrons through sharing. Let’s widen the scope of our understanding of triple bonds with the help of the following examples:

1. Dinitrogen (N≡N)

#liquid nitrogen from Ofori Concepts

The most abundant element present in the earth’s atmosphere, Nitrogen, exists mostly as odorless and colorless gas molecules of dinitrogen ( {N}_{2}) containing two nitrogen atoms linked together via triple bonds, N≡N. Nitrogen is a naturally occurring element that is essential for plants and animals for their growth. Despite its abundance (making up 78% of our atmosphere), nitrogen is largely inaccessible to plants and organisms due to its existence as dinitrogen and the presence of strong triple bonds among its atoms, making it a scarce resource and often limiting primary productivity in many ecosystems. For nitrogen to be available to make proteins, DNA, and other biologically important compounds, it must first be converted from {N}_{2} to ammonia, {NH}_{3}, by the process of nitrogen fixation. The presence of one σ and two π bonds results in the bond energy of 941 kilojoules per mole, which makes dinitrogen highly unreactive. Nonetheless, the triple bonds present in dinitrogen can break to form several compounds and coordinate complexes with metals, such as lithium and other transition metals. For a long time, researchers believed that the triple bond present in dinitrogen is the main reason for its inertness; however, new researches show that π bonds between nitrogen atoms don’t contribute much to the stability of dinitrogen, as their presence also explains the reactivity in case of acetylene. These discoveries have the potential to provide better solutions to tackle the issue of nitrogen scarcity.

2. Carbon Monoxide (:C≡O:)


Carbon monoxide is an odorless, tasteless, and colorless gas. Each carbon monoxide molecule is composed of a single carbon atom bonded to a single oxygen atom via a triple bond, accompanied by a lone pair of electrons on both atoms. In chemistry, the triple bond between carbon and oxygen in CO is considered the strongest bond with a bond energy of 1072 kilojoules per mole. In our previous example, we discussed the triple bond formed between two similar atoms; however, in the case of carbon monoxide, the two weak π bonds are slightly degenerated due to the presence of more electronegative oxygen atoms. This causes the polarization in the molecule and gives it the dipole moment, which dinitrogen does not have. The polar character of CO also contributes to its higher reactivity than nitrogen, despite having higher bond dissociation energy than the latter. Moreover, carbon monoxide is one of the most widely spread air pollutants in our atmosphere. The most important aspects of its chemistry arise from its ability to react with transition metals using a special type of chemical bond (dp-pp bonding). Carbon monoxide has a greater affinity towards the iron content in hemoglobin than oxygen because of the presence of partially polarised π bonds. This causes our blood to bind more readily to carbon monoxide than to oxygen, making our respiratory system effectively useless during contamination.

3.  Acetylene (CH≡CH)


Acetylene, also known as ethyne, is the simplest alkyne that contains two carbon atoms linked together via a triple covalent bond. It is a colorless gas that is widely used as a fuel, mainly for industrial welding purposes. In terms of valance bond theory, a triple bond among carbon atoms forms when the electrons from sp hybridized orbitals are shared among them via sigma covalent bonding, while the other two unhybridized p orbitals form weak pi bonds. This structure results in the 120.3pm of bond length among carbon atoms, which is otherwise 154 pm for single-bonded carbon-carbon atoms. The carbon-carbon triple bond places all four atoms in the same straight line, with C—CH bond angles of 180°.

4. Cyanogen (N≡C—C≡N)


Cyanogen is another organic compound that contains a triple bond; however, in this case, the triple bond exists among carbon and nitrogen atoms rather than carbon atoms. The molecular structure of cyanogens contains two cyano {[:C≡N:]}^{-} groups linked together at the carbon atoms via a single covalent bond. The bond length between the carbon and nitrogen atom is approximately 1.16 Å, whereas among carbon-carbon atoms it is 1.37 Å. Cyanogen is a colorless flammable gas that was first prepared by Sir Gay-Lussac in 1815 by the thermal decomposition of Silver Cyanide. Due to the presence of triple bonds, cyanogens contains almost the same amount of latent energy as acetylene, which can be released explosively when the compound is subjected to oxidizing agents such as fluorine, carbon monoxide, ozone, or when a mixture of cyanogen and air is subjected to a spark. Until recently, cyanogen had only been a chemical of academic interest. Several kinds of research have concluded that a stoichiometric mixture of cyanogen and oxygen can produce the hottest flames, which makes cyanogen a potential competitor for high-energy fuel.

5. Alkynes (—C≡C—)


In organic chemistry, alkynes are unsaturated hydrocarbon compounds that at least contains one triple bond linking two carbon atoms. According to the IUPAC nomenclature system, the suffix -yne is used to denote the presence of a triple bond in a hydrocarbon chain. In higher alkynes (containing four or more carbon atoms), if there is more than one triple bond present in the chain, the chain is numbered in a way such that all the triple-bonded carbon atoms get the least number positions. If the triple bond is present at either end of the chain, the alkynes are known as terminals; otherwise, they are called internal alkynes. The simplest acyclic alkynes with only one triple bond and no other functional groups form a homologous series with the general chemical formula {C}_{n}{H}_{2n−2}. In the language of valence bond theory, the carbon atoms in an alkyne bond are sp hybridized. More specifically, they each have two unhybridized p orbitals and two sp hybrid orbitals. Overlap of an sp orbital from each atom forms one sp–sp σ bond. Each p orbital on one atom overlaps one on the other atom, forming two π bonds, giving a total of three bonds. The remaining sp orbital on each atom can form a sigma bond to another atom, for example to hydrogen atoms in the case of acetylene. Almost all alkynes are odorless and colorless with the exception of ethylene, which has a slightly distinctive odor. The presence of triple bonds in alkynes contributes to their acidity, high boiling point, non-polar bonding strength, and structural linearity. The first three alkynes are gases, the next eight are liquids, and all alkynes higher than these eleven are solids.

6. Diboryne (B≡B)


It was not long ago when carbon and nitrogen were the only two elements in the periodic table that can form a stable compound with themselves featuring triple bonds. Since 2012, boron has also joined this nobility by forming stable diboryne at room temperature with two N-heterolytic carbene units attached to it. Although there are earlier reports from 2002 which show the formation of diboryne stabilized by two units of carbon monoxide in an isolation matrix, the compound was reported unstable above the temperature of -263 °C. In terms of qualitative molecular orbital theory, the B2 molecule itself is expected to have a single bond, but with NHC ligands, the third excited state yields a triple bond. There are several kinds of researches going on around the world to look for the potential applications of diboryne compounds, especially in nanomaterial sciences.

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