Chemistry · Hydrocarbons · NEET
Single bond = 1 sigma bond, 0 pi. Double bond = 1 sigma + 1 pi. Triple bond = 1 sigma + 2 pi. The rule is simple: the very first bond between any two atoms is always a sigma bond. Any extra bond drawn after that (the 2nd or 3rd line) is a pi bond. So a triple bond is not 3 pi bonds. It is 1 sigma and 2 pi.
Sigma bonds = (number of single bonds) + (number of double bonds) + (number of triple bonds), counting each multiple bond as ONE sigma. An even faster way: total sigma = (number of C-C and C-X skeleton bonds) + (number of C-H bonds). Just add up every line drawn once, plus every H attached. Then count pi separately: each double bond gives 1 pi, each triple bond gives 2 pi. This split-counting stops silly mistakes in the NEET exam.
No. A single bond is always only a sigma bond. Pi bonds only appear when there is a double bond or triple bond. This is why counting starts by marking every line as sigma first, then adding pi only for the extra lines. If a question says 'sigma bonds only', ignore all pi and just count each connection once plus the C-H bonds.
Benzene has 12 sigma bonds and 3 pi bonds. Count sigma: 6 C-C ring bonds (each counted once) + 6 C-H bonds = 12 sigma. The three alternating double bonds add 3 pi bonds (one pi each). Even though the pi electrons are delocalised, for counting you still take 3 pi bonds. Remember: a benzene ring = 12 sigma + 3 pi.
The common mistake is forgetting the C-H bonds or double-counting a multiple bond. Do it in two steps. Step 1: draw the skeleton and count each C-C link once (in pent-2-en-4-yne that is 4 links). Step 2: add every C-H bond (3+1+1+1 = 6). Total sigma = 4 + 6 = 10. Then pi: one double bond (1 pi) + one triple bond (2 pi) = 3 pi. Answer: 10 sigma, 3 pi. Always separate skeleton sigma from C-H sigma.
The number of sigma (σ) and pi (π) bonds in pent-2-en-4-yne is:
H3C-C≡CH (propyne) is passed through a red hot iron tube at 873 K to give product A. The number of sigma (σ) bonds present in the product A is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The first bond between two atoms is always sigma. Every extra bond is pi. So single = 1 sigma; double = 1 sigma + 1 pi; triple = 1 sigma + 2 pi. Count all single bonds and all C-H bonds as sigma, then add pi for the extra lines in double and triple bonds.
A triple bond has 2 pi bonds and 1 sigma bond. It is not 3 pi bonds. The very first bond is sigma; only the two extra bonds are pi.
Benzene (C6H6) has 12 sigma bonds (6 C-C + 6 C-H) and 3 pi bonds from the three alternating double bonds.
Yes. Every C-H bond is a sigma bond. Forgetting to count C-H bonds is the most common reason students get the sigma total wrong in NEET.
No. A pi bond can only form after a sigma bond is already present between two atoms. So a pi bond never exists alone; there is always a sigma bond with it.
