Here goes. I am NOT an organic chemist so please obtain other sources for information; i.e., don't take my work as gospel.

a) I believe the second one you list is more reactive because the first one is sterically hindered due to the isopropyl group. And bromine is a huge molecule, also, which means it will have extra trouble adding into the double bond. (As a funny story here, when I was in graduate school and I took organic---many, many years ago---if the question of something not reacting came up we automatically answered steric hindrance and looked for the methyl groups.:-).

For b), I am going with two as the more reactive. The oxygen is an electron withdrawing element (it has a relatively high electronegativity) and it is closer to the C=C carbons, therefore, it will have more of an effect on the C=C bond and weaken it more than will the O atom placed 1 carbon further away. And a weaker bond translates into more reactive.
Check my thinking. Check with other resources. I hope this helps.

I thought this had to do with s-character which would cause stronger bonds but it looks like the pi bonded Cs all have the same s-character.

If these were acids we could try to find which was a stronger acid and conjugate base.

Would be nice to know more about these questions. At least I might know where to look or whether I've had the information yet.

I have to go to sleep now as I've had a long day. Looks like the organic people are going to be trying you this term.

Sheryl

a) You are correct in your reasoning for the reactivity of the two compounds. The first compound is indeed sterically hindered due to the presence of the isopropyl group, which limits the accessibility of the double bond for reaction. Additionally, the large size of the bromine molecule can also pose a steric hindrance and make it more difficult for it to add into the double bond. So, the second compound is expected to be more reactive.

b) In this case, you are also correct in your analysis. The oxygen atom in the second compound is an electron-withdrawing element due to its high electronegativity. It is positioned closer to the C=C double bond, which allows it to exert a stronger electron-withdrawing effect on the double bond. This results in the weakening of the C=C bond and makes it more reactive. The oxygen atom placed one carbon further away will have a lesser effect on the double bond, making the first compound less reactive.

You have made valid points in your analysis, but it is always a good idea to cross-check with other resources to confirm the information. Organic chemistry can involve complex reactions and factors that influence reactivity, so consulting other sources can provide a more comprehensive understanding.

If you wanted to explore the concept of s-character and its effect on bond strength, it is true that the pi bonded carbons in both compounds have the same s-character. However, in this case, the sterically hindered and electron-withdrawing groups are the primary factors affecting reactivity.

If you have any specific questions or need further information, feel free to ask. Have a restful sleep!