CHEM 261 Solvents

H2O - protic or aprotic?

Protic

DMSO - protic or aprotic?

Aprotic

NH3 - protic or aprotic?

Protic

Ammonia - protic or aprotic?

Protic

Acetonitrile - protic or aprotic?

Aprotic

Acetone - protic or aprotic?

Aprotic

What factors determine nucleophilicity in protic solvents?

Size; base strength

What factors determine nucleophilicity in aprotic solvents?

Base strength

What is the strongest base in aprotic solvents?

Best nucleophile

In polar protic solvents for SN2, which is the better nucleophile? Small or large anions?

Large anions

If SN1, what is the base strength of the nucleophile?

Weak base

Can benzyl or allyl halides do SN1?

Yes

Can secondary alkyl do SN1?

No

SN1 rate law:

Rate = [Substrate]

How does polarity influence SN1 rate?

Increase

How does polarity influence SN2 rate?

Slow down

Is E1 endothermic or exothermic?

Endothermic

Is E1 endergonic or exergonic?

Exergonic at high temps

Sign on entropy (S) in elimination rxns:

Positive

E1 solvent must be (protic/aprotic)

Protic

If poor nucleophile, weak base, what reactions possible?

E1, SN1

E1 products:

Most stable alkene, leaving group, protonated solvent

What kind of base is needed for E2?

Strong base

What solvent is E2 often run in?

Aprotic

Is E2 endergonic or exergonic?

Exergonic

In E2, if strong BULKY base, what determines the product favored?

Most accessible beta hydrogens

In E2, if non-bulky strong base, what type of product?

Most stable alkene

What additional requirement exists for E2 to happen (think about beta hydrogens)

Beta hydrogen and leaving group must be anti

What substrates can be used in E2?

Primary, secondary, tertiary alkyl, allyl, benzyl (any)

What substrates favor E1?

Tertiary alkyl, allyl, benzyl

What reactions can a vinyl halide do

E2 only

Stereochemical control with HX in addition rxns?

No

Stereochemical control with H2O, H2SO4 in addition rxns?

No

stereochemical control with ROH, H2SO4 in addition rxns?

No

stereochemical control with X2 in addition rxns?

Yes, anti addition

stereochemical control with X2, H2O in addition rxns?

Yes, anti addition

stereochemical control with X2, ROH in addition rxns?

Yes, anti addition

stereochemical control with ROOOH in addition rxns?

Yes, syn addition

stereochemical control with H2, Pd/c in addition rxns?

Yes, syn addition

stereochemical control with 1. BH3, 2. H2O2, NaOH in addition rxns?

Yes, syn addition

How to identify the thermodynamic product

Most stable alkene

How to promote formation of kinetic product

Low temp

Products of alkyne + H2O + H2SO4?

Enol, tautomerizes to ketone

Products of alkyne + 1. BH3, 2. H2O2, H2O, NaOH?

Enol, tautomerizes to aldehyde

Reagents to extend carbon chain of alkyne?

1. NaNH2

2. CH3Br

Reagents to turn alkyne into cis alkene?

H2, Lindlar’s catalyst

Reagents to turn alkyne into trans alkene?

Li, NH3

Reagents to turn alkyne into alkane?

H2, Pd/C