CHEM0350 TA Solutions Week 10 Solutions Concepts Covered Alkenes Alkyne Substitution Alkyne Electrophilic Addn Tautomerization Leaving Groups

1. Alkyne Substitution Draw all possible combinations of starting materials that will react to form the following alkynes through nucleophilic substitution. a) For nucleophilic substitutions (which you’ll go more in depth about in Chapter 9), there needs to be a nucleophile (in this case, a deprotonated terminal alkyne) and an electrophile with a good leaving group. For alkynes, the carbon with the leaving group needs to be primary and sp3 hybridized. For an internal alkyne, the alkyne can be potentially be split into the starting nucleophile and the starting electrophile from either side of the alkyne: In this case, since the alkyne is symmetric, both will yield the same starting materials. *Note: I use an alkyl bromide as the electrophile, but the leaving group doesn’t necessarily have to be Br-. Other good leaving groups like other halogens would also work. b) We can do the same thing and “split” the alkyne. Lucy Jia c) CHEM0350 TA Solutions Week 10 – Tuesday The combination on the left will not work since the electrophile has the leaving group on a secondary carbon, and only primary carbons will react to yield the correct product for this reaction. d) The combination on the left will not work since the electrophile has the leaving group on an sp2 hybridized carbon, and this reaction will only work on sp3 hybridized carbons.