C4H4N – Express your answer as a chemical formula.
The Correct Answer and Explanation is:
Correct Chemical Formula: CH₃CNCH≡CH
(This is one of the valid isomers of C₄H₄N.)
Explanation
The molecular formula C₄H₄N indicates a compound made up of 4 carbon atoms, 4 hydrogen atoms, and 1 nitrogen atom. To determine its correct structural formula, we need to consider several key concepts from organic chemistry, including valency, degrees of unsaturation, and possible bonding arrangements.
First, we calculate the degree of unsaturation (DoU) using the formula: DoU=2C+2+N−H2=2(4)+2+1−42=11−42=72DoU = \frac{2C + 2 + N – H}{2} = \frac{2(4) + 2 + 1 – 4}{2} = \frac{11 – 4}{2} = \frac{7}{2}DoU=22C+2+N−H=22(4)+2+1−4=211−4=27
However, this leads to a non-integer DoU, which is unusual. This signals that the compound may contain a cyclic or aromatic structure, and more realistically, the formula may have been meant to describe C₄H₄N as a radical (with an unpaired electron) or as part of an ion (e.g., a pyrrole-type ring). However, a stable neutral isomer of C₄H₄N exists and can be drawn as crotonitrile-based or an alkyne–nitrile compound, such as CH₃–C≡C–CH=NH or CH₃–C≡N–CH=CH₂.
One of the best-known stable isomers with formula C₄H₄N is vinyl cyanide (acrylonitrile), which has the structure CH₂=CH–C≡N. But this formula is C₃H₃N, so it’s not the one in question.
A more suitable structure is CH₃–C≡N–CH=CH₂, which keeps all atoms in balance. This compound contains a nitrile group (–C≡N) and a vinyl group (CH=CH₂), offering both π-bonding and a triple bond, accounting for the high degree of unsaturation. The nitrogen is triple bonded to a carbon, and all atoms satisfy the octet rule.
In summary, C₄H₄N can be structurally represented as CH₃CNCH≡CH, a nitrile-containing unsaturated molecule, which reflects its unique bonding and electronic structure. Such compounds are often used in organic synthesis and materials science due to their reactive nitrile group.
