Could you explain “highest occupied molecular orbital” (HOMO) (It is the highest in energy orbital with electrons; usually responsible for donating electrons - GS) and “lowest unoccupied molecular orbital” (LUMO)? (It is the lowest in energy empty orbital; usually responsible for withdrawing electrons - GS).

Do acid catalyzed (No, the configuration is usually lost because of the intermediacy of a carbocation - GS). and base catalyzed (Yes - GS). opening of epoxide rings result in inversion of configuration?

Will the deprotonated acetoacetic ester attack the less substituted side of the epoxide? (Yes, it will, because it is an SN2 reaction. - GS).

Could we go over how E2 and SN2 reactions compete and how you decide which reaction will proceed? There is a portion about it from our reading homework, but I am having difficulty understanding the concept (SN2 is sensitive to nucleophilicity (+) and steric hindrance (-). E2 is favored by basicity, temperature, and stability of the C=C bond. - GS).

Professor Sereda I have a question regarding stereochemistry of acid catalyzed hydration of epoxides. I know a carbocation is formed in the make-up intermediate and they are planar; however would the nucleophile add anti the the already present OH group? Or could attack from both sides since it is planar? (It can attack from either side, which is why the second step of anti-dihydroxylation should be performed in the absence of acids.  - GS).

During Hydrogenation, will alkynes react faster than an alkene would- due to the shorter bond length of the alkyne? (Yes. The shorter carbon-carbon triple bond fits better to the length of H-H bond - GS).

Why is the hydroboration-oxidation based on steric hindrance instead of markovnikov’s rule? (Hydroboration as any other reaction proceeds by the only rule: through a lower in energy transition state. Because for the mechanism of hydroboration, Markovnikov rule does not apply to the final product of hydration - GS).

Which reactions have specific stereochemistry requirements? (All reactions that lead preferentially to a specific stereoisomer because of different energies of transition states. - GS).   How do we tell if any of them should be cis or trans? (Write the mechanism and compare energies of alternative transition states or, if appropriate, use Hammond’s postulate and look into the corresponding intermediates. - GS).

During hydration of alkynes, why does the reaction proceed to a ketone and the enol is not isolated? (Enol in this case is less stable than the carbonyl form. - GS).

In hydration or hydroboration-oxidation, is the enol considered an intermediate? (Yes. - GS). Also, can these reactions be catalyzed by either an acid or a base? (Hydroboration - no, ketonization - yes, but with very tiny amounts of the catalyst. - GS).

If we have a non-terminal alkyne and we are using hydration or hydroboration-oxidation, how do we decide where the OH group will go? (Since the Markovnikov’s rule is not applicable, you need to directly compare stabilities of intermediates or transition states. - GS).

Is the only product of trimerization a benzene ring? (Yes. - GS). Also, what is the significance of it and how does it work? (It gives access to polysubstituted benzenes and works by pulling together alkynes on the surface of a catalyst or in a coordination sphere of a metal catalyst. - GS).

What is the significance of reducing a triple bond? (Making a C=C bond with either cis- or trans-configuration by your choice - GS).

How important are oxidation reactions for alkynes, in some outside of class resources they are brought up from time to time, and do they usually just result in carboxylic acids? Thanks. (In most cases, oxidation cleaves the triple bond and converts both carbons to carboxy-groups. However, proper reagents may oxidize terminal alkynes to polyynes significant for pharmaceutical field and for astrochemistry: http://en.wikipedia.org/wiki/Polyyne  Also, combustion of alkynes provides temperatures unavailable from combustion of alkanes and alkenes.- GS).