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Capítulo 2

Alcanos:

nomenclatura,

propriedades e

(2)

Capítulo 2

Alcanos: propriedades e

aplicações

(3)

Forma dos Alcanos

(4)

Forma dos Alcanos

(5)

Isômeros constitucionais possuem propriedades

físicas (T

e

, T

f

, densidade, etc) diferentes

.

(6)

O número de isômeros constitucionais aumente

com o número de átomos de carbono

(7)

Fração

Te/

C

N

de átomos C

Gás

< 20

C

1

-C

4

Éter de petróleo

20-100

C

5

-C

7

Gasolina natural

40-205

C

5

-C

10

e alcanos cíclicos

Querosene

175-325

C

12

-C

18

e aromáticos

Óleo combustível 275-400

C

12

-C

25

Óleo lubrificante

400-500

C

25

-C

35

Asfalto

Sólidos

Compostos policíclicos

Quadro 2.1

–

Frações constituintes do petróleo

(8)

FIGURA 100 – CROMATOGRAMA DE GASOLINA COMUM COM IDENTIFICAÇÃO AUTOMÁTICA POR DHA

CONFIRMADA POR ESPECTROMETRIA DE MASSAS E IONIZAÇÃO QUÍMICA

(9)

Fontes de Metano

Uma vaca elimina de 200 a 300 litros de metano por dia = 80

milhões de toneladas por ano

(10)

Fontes de Metano

Cada cupim elimina 0,5

g/dia

= 25 kg em uma colônia = 20

(11)

n

*

nome

n

nome

1

Metano

17

Heptadecano

2

Etano

18

Octadecano

3

Propano

19

Nonadecano

4

Butano

20

Icosano

5

Pentano

21

Henicosano

6

Hexano

22

Docosano

7

Heptano

23

Tricosano

8

Octano

30

Triacontano

9

Nonano

**

31

Hentriacontano

10

Decano

40

Tetracontano

11

Undecano

41

Hentetracontano

12

Dodecano

50

Pentacontano

13

Tridecano

60

Hexacontano

14

Tetradecano

70

Heptacontano

15

Pentadecano

80

Octacontano

16

Hexadecano

100

Hectano

Tabela 2 - Nomes de Alcanos Normais

(12)

ALCANOS

NOMENCLATURA - SUBSTITUINTES

H

3

C

-H

H

3

C H

CH

3

CH

2

- Etil(a)

CH

3

CH

2

CH

2

- Propil(a)

CH

3

CH

2

CH

2

CH

2

- Butil(a)

CH

3

[CH

2

]

6

CH

2

-

Octil(a)

Isopropil(a)

H

3

C CH

CH

3

(CH

3

)

3

C

CH

3

CHCH

2

CH

3

tert-Butil(a) ou t-Butil(a)

sec-Butil(a) ou s-Butil(a)

Isobutil(a)

(CH

3

)

2

CHCH

2

(13)

ALCANOS

NOMENCLATURA - ALCANOS

RAMIFICADOS ACÍCLICOS

CH

3

CH CH

3

CH

3

Isobutano

CH

3

C CH

3

CH

3

CH

3

Neopentano

CH

3

CH CH

2

CH

3

CH

3

Isopentano

CH

3

CH

CH

3

CH

2

CH

2

CH

3

Isoexano

(14)

ALCANOS

CH

3

CH

2

CH CH

2

CH CH CH

2

CH

3

CH

3

CH

3

CH

3

2

3

4

5

6

7

7

6

5

4

3

2

1

3,4,6-Trimetiloctano (correto)

3,5,6-Trimetiloctano (incorreto)

1

8

8

1

12

11

10

9

8

7

6

5

4

3

2

2,3,3,8,9,11 - Hex ametildodecano (correto)

2,4,5,10,10,11 - Hexametildodecano (incorreto)

CH

3

CH

2

CH CH

2

CH CH CH

2

CH

3

CH

3

CH

3

CH

3

2

3

4

5

6

7

7

6

5

4

3

2

1

3,4,6-Trimetiloctano (correto)

3,5,6-Trimetiloctano (incorreto)

1

8

8

1

12

11

10

9

8

7

6

5

4

3

2

2,3,3,8,9,11 - Hex ametildodecano (correto)

2,4,5,10,10,11 - Hexametildodecano (incorreto)

(15)

ALCANOS

4-Etil-5-isopropil-2-metil-7-propildecano

1

2

3

4

5

6

7

8

9

10

4-Etil-5-isopropil-2-metil-7-propildecano

1

2

3

4

5

6

7

8

9

10

5

4

3

2

1

3-etil-2,3-dimetil-5-propiloctano

CH

2

CH

CH

2

C

CH

CH

2

CH

3

CH

3

CH

2

CH

2

CH

3

CH

3

CH

2

CH

3

CH

3

6

7

8

(16)

ALCANOS

2-metil-6- tert-butilnonano (incorreto)

6 -tert-butil-2-metilnonano (correto)

1

8

7

6

5

4

3

2

9

2-metil-6- tert-butilnonano (incorreto)

6 -tert-butil-2-metilnonano (correto)

1

8

7

6

5

4

3

2

9

(17)

ALCANOS

1,2-Dimetilciclopentano

CH

3

CH

3

Metilciclobutano

CH

3

CH

3

CH

2

CH

3 1 2 3 4 5 6

1-Etil-3-metilcicloex ano

1 2 3 4 5 6 7

4-Etil-2-metil-1-propilcicloeptano

(18)

ALCANOS

CH

3

Cl

Cloreto de metila

(CH

3

)

3

CBr

Brometo de tert-butila

Nomes não-sistemáticos, aceitos pela

IUPAC:

CHF

3

Fluorofórmio

CHBr

3

Bromofórmio

CHCl

3

Clorofórmio

CHI

3

Iodofórmio

(19)

Compostos bicíclicos

 Bicyloalkanes contain 2 fused or bridged rings

 The alkane with the same number of total carbons is

used as the parent and the prefix bicyclo- is used

 The number of carbons in each bridge is included in the

middle of the name in square brackets

(20)

ALCANOS

Estereoisomeria em compostos cíclicos

 Primário: encontra-se ligado apenas a outro átomo de carbono.

 Secundário: encontra-se ligado a outros dois átomos de carbono.

 Terciário: encontra-se ligado a outros três átomos de carbono.

 Quaternário: encontra-se ligado a outros quatro átomos de carbono.

H

3

C

C

CH

2

CH

CH

3

CH

3

CH

3

CH

3

1

2

3

4

5

6

7

8

(21)
(22)

Análise conformacional do butano

A rotação em torno da ligação C2-C3 resulta

em seis conformações importantes

(23)

ALCANOS

Isomeria em alcanos cíclicos

CH

3

H

CH

3

H

H

H

CH

3

H

H

CH

3

H

H

(I)

(II)

Br Br Br

trans-1-bromo-3-tert-butilcicloexano

cis-1,2-dibromociclobutano

(24)

The Origin of Ring Strain in Cyclopropane and

Cyclobutane : Angle Strain and Tortional Strain

Angle strain is caused by bond angles different from 109.5

o

Tortional strain is caused by eclipsing C-H bonds on adjacent

carbons

Cyclopropane has both high angle and tortional strain

Cyclobutane has considerable angle strain

It bends to relieve some tortional strain

Cyclopentane has little angle strain in the planar form but bends

(25)

Chapter 4

25

Conformations of Cyclohexane

The chair conformation has no ring strain

(26)

The boat conformation is less stable because of flagpole

interactions and tortional strain along the bottom of the boat

The twist conformation is intermediate in stability between the

(27)

Chapter 4

27

Substituted Cyclohexanes: Axial and Equatorial

Hydrogen Atoms

Axial hydrogens are perpendicular to the average plane of the ring

Equatorial hydrogens lie around the perimeter of the ring

The C-C bonds and equatorial C-H bonds are all drawn in sets of

parallel lines

(28)

The Origin of Ring Strain in Cyclopropane and

Cyclobutane : Angle Strain and Tortional Strain

Angle strain is caused by bond angles different from 109.5

o

Tortional strain is caused by eclipsing C-H bonds on adjacent

carbons

Cyclopropane has both high angle and tortional strain

Cyclobutane has considerable angle strain

It bends to relieve some tortional strain

Cyclopentane has little angle strain in the planar form but bends

(29)

Chapter 4

29

Conformations of Cyclohexane

The chair conformation has no ring strain

(30)

The boat conformation is less stable because of flagpole

interactions and tortional strain along the bottom of the boat

The twist conformation is intermediate in stability between the

(31)

Chapter 4

31

Substituted Cyclohexanes: Axial and Equatorial

Hydrogen Atoms

Axial hydrogens are perpendicular to the average plane of the ring

Equatorial hydrogens lie around the perimeter of the ring

The C-C bonds and equatorial C-H bonds are all drawn in sets of

parallel lines

(32)

Methyl cyclohexane is more stable with the methyl equatorial

An axial methyl has an unfavorable 1,3-diaxial interaction with axial C-H bonds 2 carbons away

(33)

Chapter 4

33

Disubstitued Cycloalkanes

Can exist as pairs of cis-trans stereoisomers

Cis: groups on same side of ring

(34)

Trans-1,4-dimethylcylohexane prefers a

trans-diequatorial conformation

(35)

Chapter 4

35

Cis-1,4-dimethylcyclohexane exists in an axial-equatorial

conformation

A very large tert-butyl group is required to be in the more stable

(36)

Bicyclic and Polycyclic Alkanes

The bicyclic decalin system exists in non-interconvertible cis and

(37)

ALCANOS

Isomeria

(38)

ALCANOS

Isomeria

(39)

ALCANOS

Reações - Formação de Radicais

R

3

C

+

Homólise

X

R

3

C

X

Estabilidade relativa dos radicais alquila simples

R

C

R

R

>

R

C

>

R

H

H C

H

H

>

R

C

H

H

(40)
(41)

ALCANOS

Reação - Halogenação

CH

4

+

Cl

2

(ex)

ou

CH

3

Cl

+ CH

2

Cl

2

+

CH

Cl

3

+ C

Cl

4

+ H

Cl

h

Mecanismo da cloração do metano

Término

+

Cl

2

Cl

2

+

CH

3

Cl

+

CH

3

CH

3

Propagação

+ CH

4

+ HCl

+

CH

3

Cl +

CH

3

Cl

Cl

CH

3

H° = -106,7 kJ mol

-1

H° = 3,4 kJ mol

-1

Iniciação

Cl

2

2

Cl

Hº = 242,7 kJ mol

-1

Cl

Cl

Cl

CH

3

CH

3

CH

3

H° = -242,7 kJ mol

-1

H° = -349,4 kJ mol

-1

H° = -368,2 kJ mol

-1

(42)

REAÇÕES DE ALCANOS

Monobromação do metilpropano

O

XIDAÇÃO

DE

ALCANOS

Traços

CH

3

CH CH

2

Br

CH

3

+

> 99%

CH

3

C

CH

3

CH

3

Br

C

127

o

Br

2

CH

3

C

CH

3

CH

3

H

C

n

H

2n+2

~55 kJ g

-1

de

hidrocarboneto

+

H

2

O

(n+1)

+

CO

2

n

O

2

2

3n+1

+

C

4

H

10

(g)

+ +

10 H

2

O(l)

8 CO

2

(g)

13 O

2

(g)

CH

4

(g)

+

2 O

2

(g)

CO

2

(g)

+

2 H

2

O(l)

H = -891,2 kJ mol

-1

H = -2878,6 kJ mol

-1

ALCANOS

(43)

P

IRÓLISE

, I

SOMERIZAÇÃO

E

C

ICLIZAÇÃO

Reação de pirólise

C C H H C H H C C H H C H H H H C C H H C H H C H H C H H H H C C H H C H H H C H H C H H H H H H H Aquecimento C C H H C H H H H C C H H C H H H C H H C H H H H H C C H H C H H C C H H C H H H H C H H C H H H H + C C H H C H H H H C C H H C H H H C H H C H H H H C C H H C H H C C H H C H H H H C H H C H H H H H

Figura 2.5 – Esquema representando a pirólise do hexadecano.

(44)

R

EAÇÃO

DE

I

SOMERIZAÇÃO

2-metileptano

H

3

C CH

2

CH

2

CH

3

H

3

CCH

2

CH

2

CH

2

CH

2

CH

2

CH

2

CH

3

H

3

CCHCH

2

CH

2

CH

2

CH

2

CH

3

CH

3

H

3

C CH CH

3

CH

3

AlCl

3

27 ºC

Isobutano

Figura 2.7 – Exemplos de reações de isomerização

de alcanos

(45)

REAÇÕES DE ALCANOS

R

EAÇÃO

DE

C

ICLIZAÇÃO

Figura 2.8 - Reações de ciclização de alcanos.

- 4 H

2

- 3 H

2

Tolueno

Referências

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