number of possible(strutural isomars)alkynes with C5H6

The formula C5H6 corresponds to a degree of unsaturation of 4. This means that the molecule can have 4 pi bonds, or 3 pi bonds and a ring, or 2 pi bonds and 2 rings, or 2 pi bonds and a cyclopropane ring, or 1 pi bond and 3 rings, or 4 rings.

However, since we are looking for alkynes, we are interested in structures with triple bonds. A triple bond counts as 2 pi bonds, so we are looking for structures with 2 triple bonds, or 1 triple bond and 1 pi bond, or 1 triple bond and a ring.

1. Structures with 2 triple bonds: There is only one way to arrange 2 triple bonds in a 5-carbon chain, which is to put them at the ends of the chain. This gives us 1 structure.

2. Structures with 1 triple bond and 1 pi bond: There are 3 ways to arrange this. The triple bond can be at the end of the chain and the pi bond can be at one of the 3 remaining positions, or the triple bond can be at the second position and the pi bond can be at one of the 2 remaining positions, or the triple bond can be at the third position and the pi bond can be at the end of the chain. This gives us 3 structures.

3. Structures with 1 triple bond and a ring: There are 2 ways to arrange this. The triple bond can be at the end of the chain and the remaining 4 carbons can form a ring, or the triple bond can be at the second position and the remaining 3 carbons can form a ring. This gives us 2 structures.

So in total, there are 1 + 3 + 2 = 6 possible structural isomers of C5H6 that are alkynes.