Will you please explain the difference between cationic polymerization of alkenes and free radical polymerization of alkenes. And how that compares to addition of HCl to alkenes. (Both cationic polymerization and electrophilic addition of HCl start from protonation  of C=C. Radical polymerization starts from the attack of C=C by a free radical. - GS).

I was reviewing through the lecture slides and came across the following question: Why do we not consider absorption of IR by N2 and O2, which are way more abundant in the atmosphere, then CO2? Is the answer because N2 and O2 are symmetrical, unlike CO2, and therefore they have a negligible dipole moment; and, with IR absorption such as in IR spectroscopy, a dipole moment must be present in order for IR to be absorbed? Thank you. (Almost. We need to consider change of the dipole moment, not the dipole moment itself. - GS).

Why is carbon 13 used instead of carbon 12 for NMR? (Because Carbon 13 is magnetic, and carbon - 12 is not. - GS).

In hydrobromination in the presence of peroxide, does the hydrogen or bromine connect to the carbon of the c=c? (Both, just like in any addition to C=C. - GS).

Which one connects first, the hydrogen or bromine? (Bromine. - GS).

Do bromonium cations only form with cyclic compounds, or would it also form for straight chain alkenes? (Any compound shape. - GS).

How would the free-radical addition of Br-Br to cyclohexene compare to the non-free radical addition? (Under free-radical conditions, Br2 will substitute an allylic hydrogen rather than add to C=C. NBS is even a better reagent for free radical halogenation. - GS). Why does it substitute an allylic hydrogen instead of adding to the C=C? (Because abstraction of an allyl hydrogen leads to a stable allyl radical, so the reaction pathway shifts to the more favorable substitution over addition. Some addition still takes place, and this is suppressed by using NBS instead of Br2. - GS).

Should we be able to predict carbocation rearrangements, or just know how/why they occur? (Yes., You can predict the rearrangement, if there is a pathway to a more stable carbocation by the following mechanism: http://ochem.orgfree.com/rear.html   - GS.