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Alicyclics Aliphatic compounds containing rings, cycloalkanes, cycloalkyl halides, cycloalkyl alcohols, cyclic ethers, cycloalkenes, cycloalkadienes, etc. Cycloalkanes. cyclopropane cyclobutane cyclopentane cyclohexane . methylcyclopentane 1,1-dimethylcyclobutane.

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slide1

Alicyclics

Aliphatic compounds containing rings, cycloalkanes, cycloalkyl halides, cycloalkyl alcohols, cyclic ethers, cycloalkenes, cycloalkadienes, etc.

slide2

Cycloalkanes

cyclopropane cyclobutane cyclopentane cyclohexane

slide3

methylcyclopentane 1,1-dimethylcyclobutane

trans-1,2-dibromocyclohexane

slide5

cycloalkenes

3

4

2

5

1

6

cyclopentene 3-methylcyclohexene 1,3-cyclobutadiene

slide7

Cycloalkanes, syntheses:

  • Modification of a ring compound:
  • 1. reduction of cycloalkene
  • 2. reduction of cyclic halide
  • a) hydrolysis of Grignard reagent
  • b) active metal & acid
  • 3. Corey House
  • B. Ring closures
slide8

A. Modification of a cyclic compound:

H2, Ni

Sn, HCl

Mg; then H2O

slide9

Li

CuI

+ CH3CH2-Br

CH2CH3

must be 1o

Corey-House

slide10

ring closures

  • CH2=CH2 + CH2CO, hv 
  • Br-CH2CH2CH2CH2CH2-Br + Zn 
  • etc.
slide11

cycloalkanes, reactions:

  • halogenation
  • 2. combustion
  • 3. cracking
  • 4. exceptions

Cl2, heat

+ HCl

slide12

exceptions:

H2, Ni, 80o

CH3CH2CH3

Cl2, FeCl3

Cl-CH2CH2CH2-Cl

H2O, H+

CH3CH2CH2-OH

conc. H2SO4

CH3CH2CH2-OSO3H

HI

CH3CH2CH2-I

slide13

exceptions (cont.)

+ H2, Ni, 200o CH3CH2CH2CH3

??????????

slide14

internal bond deviation heat of

angles from 109.5 combustion

60o-49.5o 166.6

90o-19.5o 164.0

108o -1.5o158.7

slide15

Cyclopropane undergoes addition reactions that other cycloalkanes and alkanes do not. This is because of angle strain in the small ring. Because the bond angles are less than the optimal 109.5o for maximum overlap, the bonds are weaker than normal carbon-carbon single bonds and can be added to.

Cyclobutane has angle strain that is less than that for cyclopropane, reacts with H2/Ni at a higher temperature, but does not react like cylcopropane in the other exceptional reactions.

slide16

internal bond deviation heat of

angles from 109.5 combustion

60o-49.5o 166.6

90o-19.5o 164.0

108o -1.5o158.7

120o +11.5o157.4

128.5o +19o158.3

135o +25.5o158.6

slide17

Cyclohexane does not have any angle strain! It isn’t a flat molecule. By rotating about the carbon-carbon bonds, it can achieve 109.5o bond angles.

slide18

conformations of cyclohexane

chair twist boat

boat

slide19

The chair conformation of cyclohexane is free of both angle strain and torsional strain (deviation from staggered). This is the most stable conformation.

slide20

The boat conformation is free of angle strain, but has a great deal of torsional strain (eclipsed). To relieve the strain, it twists slightly to form the twist boat:

slide23

CH3 in axial position CH3 in equatorial position

is more stable

slide25

Cycloalkenes, syntheses:

  • Modification of a ring compound:
  • 1) dehydrohalogenation of an alkyl halide
  • 2) dehydration of an alcohol
  • 3) dehalogenation of vicinal dihalides
  • (B. Ring closures)
slide26

KOH(alc)

H+, Δ

cyclohexene

Zn

slide27

Cycloalkenes, reactions:

  • addition of H2 8. hydroboration-oxid.
  • addition of X2 9. addition of free radicals
  • addition of HX 10. addition of carbenes
  • addition of H2SO4 11. epoxidation
  • addition of H2O,H+ 12. hydroxylation
  • addition of X2 + H2O 13. allylic halogenation
  • oxymerc-demerc. 14. ozonolysis
  • 15. vigorous oxidation
slide28

H2, Pt

Br2, CCl4

trans-1,2-dibromocyclohexane

slide30

HBr

H2SO4

H2O, H+

Markovnikov orientation

slide31

Br2 (aq.)

H+, dimer.

HF, 0o

slide33

HBr, peroxides

polymerization

CH2CO, hν

Peroxybenzoic acid

slide34

KMnO4

cis-1,2-cyclohexanediol

HCO3H

trans-1,2-cyclohexanediol

Br2, heat

slide38

NaOH

2o alkyl halide => E2

Mg

H2O

conc. HI, heat

conc. HBr, heat

2 Br-CH2CH2-Br

1,4-dioxane

slide39

Alicyclic compounds are chemically like their open chain analogs. The exceptions are for small ring compounds where angle strain may give rise to reactions that are not typical of other molecules.

slide40

Epoxides:

ethylene oxide propylene oxide cyclopentene oxide

(oxirane) (methyloxirane)

Synthesis:

C6H5CO3H

cis-2-butene

β-butylene oxide

slide41

epoxides, reactions:

  • acid catalyzed addition

OH

CH2CH2

OH

H2O, H+

OH

CH3CH2-O-CH2CH2

CH3CH2OH, H+

OH

CH2CH2

Br

HBr

slide42

2. Base catalyzed addition

OH

CH2CH2

OH

CH3CH2-O-CH2CH2-OH

H2N-CH2CH2-OH

CH3CH2CH2CH2-OH

slide45

acid catalyzed addition to unsymmetric epoxides?

OH

+ H2O, H+ CH3CHCH2

OH

which oxygen in the product came from the water?

18OH

CH3CHCH2

OH

+ H218O, H+

slide46

CH3

O

+ CH3OH,H+ CH3CHCH2

OH

Br

+ HBr  CH3CHCH2

OH

slide47

Base?

18OH

+ Na18OH, H218O CH3CHCH2

OH

OCH3

+ CH3OH, CH3ONa CH3CHCH2

OH

NH2

+ NH3 CH3CHCH2

OH

slide48

Acid:

Z

+ HZ CH3CHCH2

OH

Base:

Z

+ Z-, HZ CH3CHCH2

OH

slide49

“variable transition state”

Z

acid: — C — C —

OH

Bond breaking is occurring faster than bond making, making the carbon slightly positive. C δ+ : 3o > 2o > 1o

δ+

δ+

base:

Z

— C — C —

O

Bond breaking is occurring at the same time as bond breaking, there is no charge on the carbon. Steric factors are most important: 1o > 2o > 3o

δ-

slide50

Acid:

Z

+ HZ CH3CHCH2

OH

Cδ+: Z to 2o carbon

Base:

Z

+ Z-, HZ CH3CHCH2

OH

steric factors: Z to 1o carbon

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