Ochem rxns + enantiomers

[medworm]

Suppose I don't recall the mechanism of a rxn -- how can I tell from the passage? Is there some simple way of remembering this?

For example, if a reagent converts a compound into a Nucleophile, it can: abstract a proton, protonate a poor leaving group, attack the carbonyl carbon, attack the alpha-hydrogen and so forth.

What's done in each case??
alcohol
aldehyde
ketone
carb. acid
acyl halide


Also, to find the enantiomer of a compound, do I just flip the direction of ALL the wedges that go in and out of the page?

Thanks.

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[medworm]

I've done some research/review and I'm going to answer my own Qs, in case anyone else have the same Q later.

Generally...

ALCOHOL
Protonate OH into better LG (H20), carbocation rearranges to form new C=C bond. Make ROH by adding H20 to C=C double bond. Reduce carb. derivatives to ROH w/ LiAlH4 and NaBH4. Oxidize ROH w/various agents into carb. derivatives.

ALDEHYDE/KETONE
Ald/ketone is E-phile. Electron from C=O delocalizes onto Oxygen, makes O-. In Nu Addn rxn, Nu attacks highly reactive carbonyl carbon, forms tetrahedral intermediate w/ O-, which gets protonated to become ROH. Ald/ketone + ROH makes hemiacetal and acetals.

ALDOL CONDENSATION
Enolate ion (O-) acts as Nu which attacks carbonyl carbon (C=O). Electron delocalizes onto Oxygon, makes O- which gets protonated. Rxn makes an aldol, which has C=O and OH on opposite ends of molecule. Dehydration yields additional conjugation.

CARB ACID + DERIVATIVES
Reacts via Nu Substitution, which is similar Nu Addn rxn (above). Nu attacks carbonyl carbon, delocalize electrons onto Oxygen making it O-. Forms unstable tetrahedral intermediate, where the weakest group gets protonated and leaves. Oxygen pushes e- back towards center carbon and reforms C=O. So in other words, the Nu substitutes the LG group.

CLAISEN CONDENSATION
Like Aldol Condensation, enolate adds to carbonyl carbon of another ester. Forms unstable tetrahedral intermediate, which forces ethoxide to leave.


ENANTIOMERS
To find the enantiomer of a compound, flip the direction of ALL the wedges that go in and out of the page.

 

[Turkeyman]

A lot of times they'll tell you that stuff in the passage itself. Or at the least they'll tell you enough information such that you can infer things about the mechanism i.e. it goes through a carbocation intermediate, which means you should immediately be like AHA its SN1, possible skeletal re-arrangement, a group leaves on its own, etc etc

 

[jon0013]

when deciding between E1 and E2 do we just base it off solvent? polar protic=E1 and polar aprotic=E2?

i remember that there was a kaplan question that said E1 is favored by acidic solvent..the only reasoning i could think of was E1 only depends on alkyl halide concentration while E2 needs a strong base as well as alkly halid concentration...correct me if i am wrong