Chemistry · General Principles Of Organic Chemistry · NEET
No. A single bond is always just 1 sigma bond and 0 pi bonds. Pi bonds only appear as the extra bonds inside a double or triple bond. So if a molecule has only single bonds (like ethane or methane), the pi count is zero.
A double bond = 1 sigma + 1 pi (2 bonds total, but only 1 sigma). A triple bond = 1 sigma + 2 pi (3 bonds total, but still only 1 sigma). The first line is always the sigma bond; every extra line is a pi bond.
Benzene has 6 C-C bonds in the ring plus 6 C-H bonds = 12 sigma bonds. It has 3 pi bonds (three double bonds in the Kekule structure). So benzene = 12 sigma + 3 pi. Count every bond line as one sigma, then add the extra lines as pi.
A triple bond has 2 pi bonds, not 3. The three lines are made of 1 sigma bond and 2 pi bonds. Students often wrongly count 3 pi. Remember: total lines minus 1 (the sigma) gives the pi count for that bond.
No. Lone pairs are non-bonding electrons and are not sigma bonds. Only shared bonding pairs (actual bond lines between two atoms) count. A lone pair does affect hybridisation, but it is never a sigma or pi bond.
The number of sigma and pi bonds in pent-2-en-4-yne is
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Count every bond line in the structure (all C-C, C-H, C-O, etc.). Each line, whether it is part of a single, double, or triple bond, contributes exactly 1 sigma bond. So the total number of connections between atoms equals the number of sigma bonds.
Count double bonds and triple bonds only. Each double bond gives 1 pi bond and each triple bond gives 2 pi bonds. Add them: pi = (double bonds) + 2 x (triple bonds). Single bonds contribute zero pi bonds.
The first (head-on) overlap of orbitals along the bond axis forms the strong sigma bond. Any additional bonding must use sideways (parallel) overlap of p-orbitals, which forms weaker pi bonds. That is why the first line is sigma and the rest are pi.
Ethyne is H-C#C-H. It has 3 sigma bonds (two C-H and one C-C sigma) and 2 pi bonds (from the triple bond). This is a classic NEET example.
Yes, indirectly. The number of sigma bonds plus lone pairs on an atom decides its hybridisation (2 = sp, 3 = sp2, 4 = sp3). Pi bonds do not change hybridisation. NEET often links bond counting with hybridisation in the same question.
