Chem 51B Stuff

-10.0

HI

-9.0

* HBr

-7.0

HCl

-5.0

H2SO4

-2.5

CH3OH2 (+)

-1.7

* H3O (+)

-0.6

benzene-SO3H

3.2

HF

4.8

* CH3COOH (carboxylic acid)

7.0

H2S

9.1

HCN

9.4

NH4 (+)

10.5

* CH3CH2SH

10.8

* (CH3)3NH (+)

15.5

* CH3OH

25

HCCH (Alkyne)

36

* NH3

about 40

H2 (gas)

pKa of Acetic acid

5

pKa of Ethanol

16

Which is an Alcohol?

Which is an Amide?

Which is an Amine?

What’s the difference between an amide and an amine?

amide has a nitrogen attached to a carbonyl (C=O) and an amine has a nitrogen attached to a functional group or to hydrogens

SN2 happens by

backside attack

E2 happens by

antiperiplanar (newman projection)

Substrates that can do SN2 rxns

CH₃>1˚>2˚

Substrates that can do SN1 rxns

3˚>2˚

Nucleophiles that can do SN2 rxns

Strong ones (ex: stuff with opposite charges, CN, N₃, Cl^-, Br^-, RS^-, HS^-, H₂S)

Leaving group rankings for SN2, SN1, E1, and E2 rxns

OT^- > I^- > Br^- > Cl^-

Nucleophiles that can do SN1 rxns

Weak ones can (ex: H₂O, ROH, RCOOH)

Substrates that can do E2 rxns

3˚>2˚>1˚

Substrates that can do E1 rxns

3˚>2˚

Bases that can do E2 rxns

Strong bases and strong bulky bases (ex: OH^-, RO^-, t-butO^-, DBN)

Stereochemistry for E2 rxns

the H and leaving group HAVE to be antiperiplanar

Bases that can do E1 rxns

weak nucleophiles/bases (ex: H₂O, ROH, RCOOH)

Zaitsev’s Rule

In an E1 or E2 elimination reaction, the major product is the most substituted alkene, like how many alkyl groups (CH₃) are attached to one carbon, the more that are attached the more stable the product

How do we react alcohols?

We protonate the alcohol with an acid first, so then the leaving group can become H₂O and form a carbocation

E1 reaction with an alcohol

Called a dehydration where a water is removed, more stable carbocation (3˚) will get a faster rxn, will use an acid like H₂SO₄

Why can’t an SN1 reaction happen with dehydration?

H₂SO₄ is a weak nucleophile and very stable, which never traps a cation

Why do we use H₂SO₄ for E1 alcohol rxns?

It’s a conjugate base and a poor nucleophile

E2 reactions with alcohols

needs really strong reagents for alcohols to form, CAN’T USE ACIDS CUZ IT WILL MAKE A CATION, will use something like POCl₃ and pyridine to react

How does an E2 with an alcohol work?

More substituted alcohol (3˚) will get the faster rxn, H and leaving group HAVE to be antiperiplanar

SN1 reactions of alcohols

usually happen with a carbocation (HX - HCl, Hbr, HI)

When deprotenating an alcohol

You need NaH or PBr₃ and it will ALWAYS do SN2 rxns

Do Ts and CN’s react the same or differently?

They perform an SN2 the SAME

Where does the nucleophile attack an epoxide in acidic conditions?

More substituted carbon, will do SN2 to break open the ring by using an acid to protenate the oxygen under acidic conditions. Order to go by: 3˚>1˚>2˚

Where does the nucleophile attack an epoxide in basic conditions?

less substituted product, will do SN2 to break open the ring, usually uses strong nucleophiles (ex NaOCH₃

What type of reaction is this?

E2

What type of reaction is this?

E2

What type of reaction is this?

E1 because H₂SO₄ is reacting on an alcohol

What type of reaction is this?

E2

What type of alkene reaction is this?

Hydroboration

What type of alkene reaction is this?

Hydration

What type of alkene reaction is this?

Halogenation

What type of alkene reaction is this?

Halohydration Formation

What type of alkene reaction is this?

Hydroboration-oxidation

What type of structures do Hydrohalogenation and Hydration reactions make?

Make both Syn and Anti, usually happens under acidic conditions, does Markovnikov addition

What type of structures do Halogenation and Halohydrin Formation reactions make?

Makes Anti, initiated with either Cl₂ or Br_2, does Markovnikov addition

What type of structures do hydroboration-oxidation reactions make?

Makes Syn, usually initiated with BH₃ and then H₂O₂ and HO^-, does anti-Markovnikov addition

Markovnikon vs Anti-Markovnikov

Markovnikov - places nucleophile on the more substituted C

Anti-Markovnikov - places nucleophile on less substituted C

What type of alkyne reaction is this?

Hydrohalogenation, does Markovnikov addition

What type of alkene reaction is this?

halogenation, tetrahalide, does Markovnikov addition

What type of alkene reaction is this?

hydration, makes ketones, does Markovnikov addition

What type of alkene reaction is this?

Hydroboration-oxidation, makes aldehydes and does Anti-Markovnikov addition

Keto-Enol Tautomerization with an acid

Keto-Enol Tautomerization with a base

pH?

5

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Difference between SN1 and SN2 Reactions

SN2 reactions are usually done in 1 step using strong nucleophiles (ex: CN-), Cl-, Br-, etc…) substrates like methyls, and 1˚ ones usually do it, does an inversion

SN1 reactions are usually two step with an intermediate, uses weak nucleophiles (ex: H₂O, ROH, etc) products are usually racemic, subtrates like 3˚ and 2˚ do it.

Addition via Ionic Intermediates

Substitution via radical intermediates

H bonds to the less substituted C

Br bonds to the less substituted C

Order of worst to best leaving group in an E2 reaction

F^-< Cl^- < Br^- < I^-

Dehydration from Alcohols to Alkenes

E2 Reaction, must be with a weak base and good leaving group, must convert alcohol from a poor leaving group to a good one, uses H2SO4 or TsOH to do it

How do you make a molecule into an alkyne from an alkane

2 equivalents of NaNH2 to turn a molecule into an alkyne