2.32 Female tiger moths signify their presence to male moths by giving off a sex attractant. The sex attractant has been isolated and found to be a 2-methyl-branched alkane having a molecular weight of 254. What is this material?

Dear Student,

This material is 2-methylheptadecane. It is an alkane containing 17 carbons with a methyl branch at second carbon. Its formula is C₁₈H₃₈.

Explanation:
As per question,

• the material is an alkane, so, its general formula will be C_nH_2n+2
• Molecular weight of the alkane is 254, so, mass of  C_nH_2n+2 = 254.

Now, atomic mass of C = 12 and H = 1
Using these atomic masses in general formula to get molecular mass, 
12 (n) + 1 (2n+2) = 254
12n +2n + 2 = 254
14n = 252
n = 18
So, the formula becomes C₁₈H₃₈

Also, given in question, it has 2-methyl branch which means, the compound has 17 carbon saturated chain with methyl branch at carbon number 2.
 
The structure is 



Regards.