CHEM 351 Poole Exam 3 Reactions to Memorize

What mechanism does SOCl2 use to deal with alcohols?

SN2; only works with primary and secondary alcohols

What product is formed from an alcohol reacting with SOCl2 and pyridine?

Alkyl chloride, inversion of stereochemistry on stereocenter

What mechanism does PBr3 use to deal with alcohols?

SN2; only works with primary and secondary alcohols

What product is formed from an alcohol reacting with PBr3?

Alkyl bromide, inversion of stereochemistry on stereocenter

What mechanism does TsCl use to deal with alcohols?

SN2; only works with primary and secondary alcohols

What product is formed from an alcohol reacting with TsCl and pyridine?

A tosylate (R-OTs), which is a good leaving group, RETENTION of stereochemistry on stereocenter; can then be reacted with any other good nucleophile

What mechanism does TsOH (or H2SO4) use to deal with alcohols?

E2 for primary alcohols, E1 for secondary and tertiary alcohols

What product is formed from an alcohol reacting with TsOH (or H2SO4)?

Alkene(s), can be multiple if there are multiple beta protons

What mechanism does POCl3 use to deal with alcohols?

E2

What product is formed from an alcohol reacting with POCl3 and pyridine?

Alkene(s), can be multiple if there are multiple beta protons

What mechanism does an acid (HI, HCl, HBr) use to deal with alcohols?

Protonation of alcohol to convert it into a good leaving group; THEN SN2 for primary alcohols, SN1 for secondary and tertiary alcohols

What product is formed from an alcohol reacting with a halogen acid (like HBr)?

SN2: alkyl halide, inversion of stereochemistry on stereocenter

SN1: alkyl halide, 1:1 mixture of isomers based on top or bottom attack of halide

In epoxide opening, what C will the nucleophile prefer to attack under normal/basic conditions?

The reaction is SN2, so it will prefer to attack the less subsistuted C

In epoxide opening, what C will the nucleophile prefer to attack under acidic conditions?

Like SN1 it will prefer to attack the more substituted C because the oxygen is electron-rich and so the partial positive charge will go on the more substituted carbon and the A- will be attracted to it

Mechanism of alkene hydrohalogenation

Pi attacks H of acid (HBr, HCl) from top or bottom

H+ goes on less substituted carbon, leaving a more substituted carbocation

A- attacks either top or bottom of carbocation

Mechanism of acid-catalyzed alkene hydration

Acid protonates H2O

Pi attacks H of protonated H3O+ from top or bottom

H+ goes on less substituted carbon, leaving a more substituted carbocation

H2O attacks top or bottom of carbocation, is then deprotonated to form an OH group

Mechanism of halogenation

Pi attacks Br2 AND Br attacks one side of the alkene, forming a bromonium intermediate

Behaves like an epoxide, Br- forms SN2 backside attack

ONLY anti products because of backside attack

Mechanism of halohydrin formation

Same as halogenation, but for the backside attack instead of A-, H2O attacks and then is deprotonated

H2O or ROH attacks more substituted carbon because it holds more positive charge from the halonium ion +

ONLY anti products because of backside attack

Mechanism of hydroboration-oxidation

Hydroboration:

Pi attacks empty p of BH3,

H- on more substituted carbon with partial + charge

BH2 on other carbon, ONLY syn products

Oxidation:

MECHANISM NOT NEEDED, BH2 replaced with OH with retention of stereochemistry

Reduction of alkynes or alkenes with Pd/C

Reduces all the way to alkane, syn addition of H2 either on top or bottom

Reduction of alkynes with Lindlar catalyst

Cis alkene product

Reduction of alkynes with Na, NH3

Trans alkene product

What is LiAlH4?

A strong reducing agent, can be used to open epoxides with an SN2 reaction mechanism

What is mCPBA?

Syn addition of an epoxide to both sides of the double bond of an alkene (cis if cis, trans if trans)

Mechanism of anti-dihydroxylation

Form an epoxide with mCPBA, then open with water backside attack to form ONLY anti diol products

What is the use of OsO4, NaHSO3 and H2O?

Syn-dihydroxylation (2 steps)

What reagents can you use to oxidize a secondary alcohol into a ketone?

PCC, CrO3 (with H2SO4 and H2O)

What reagent can you use to oxidize a primary alcohol into an aldehyde?

PCC dissolved in CH2Cl2 (no water, so can't form aldehyde hydrate and oxidize again to carboxylic acid)

What reagents can you use to oxidize a primary alcohol into a carboxylic acid?

CrO3 with H2SO4 and H2O

(mechanism same as PCC to start, but then water forms the aldehyde hydrate form which allows it to oxidize again into a carboxylic acid)