3.1 Functional Groups - Yonsei University · 2017-11-13 · Ch.3 Organic Compounds: Alkanes and Cycloalkanes functional groups: a group of atoms within a molecule that has a characteristic

Ch.3 Organic Compounds: Alkanes and Cycloalkanes

functional groups: a group of atoms within a molecule that has a characteristic chemical behavior; a given functional group, regardless of size and complexity, behaves in nearly the same way

3.1 Functional Groups

• more than 19 million known organic compounds according to Chemical Abstracts

• classify into families with similar chemical behavior


H

H

H

H

HO

Ethylene

Cholesterol

Br2 H

H

H

H

HO

Br

Br

BrBr

Br2


Functional Groups

Alkane Alkene

C C

Alkyne

C C

Arene(aromatic ring)

C C

Functional Groups with C/C Multiple Bonds

C/C Multiple BondsC-Y (Y= electronegative atom: O, N, Cl, S...)C=O, C=N, C≡N


Functional Groups with C-Y (Y= electronegative atom)

Halide

XC

(X= F, Cl, Br, I)Alcohol

OHC

Ether

OC C

Amine

NH2C

SulfideThiol

SHC SC C


Functional Groups with C=O

Aldehyde

CC HO

Ketone

CC CO

Carboxylicacid

CC OHO

Ester

CC OO

C

Amide

CC NO

Carboxylicacid chloride

CC ClO


Table 3.1 Structures of Common Functional Groups

Familyname

Functional groupstructure

Simple example Name ending

Alkane contains only C-H and C-C single bonds CH3CH3

-aneEthane

Alkene C C CH2=CH2

-eneEthene

(Ethylene)

Alkyne C C-yne

Ethyne(Acetylene)

C CH H

Arene NoneBenzene



Familyname



Halide XC NoneChloromethane

ClH3C(X= F, Cl, Br, I)

Alcohol OHC -olMethanol

OHH3C

Ether OC -etherDimethyl ether

OH3CC CH3



Familyname



Amine NHC -amineMethylamine

NH2H3C

Nitrile CC-nitrile

Ethanenitrile(Acetonitrile)

CH3CN N

NCNH2C

Nitro NO2C NoneNitromethane

NO2H3C



Familyname



Sulfide -sulfideDimethyl sulfide

Thiol SHC -thiolMethanethiol

SHH3C

SC C SH3C CH3

Sulfoxide -sulfoxideDimethyl sulfoxideSC C SH3C CH3

O O

Sulfone -sulfoneDimethyl sulfoneSC C SH3C CH3

O O

O O



Familyname



Aldehyde-al

Ethanal(Acetaldehyde)

CC H CH3C H

O O

Ketone-one

Propanone(Acetone)

CC C CH3C CH3

O O

Carboxylicacid

-oic acidEthanoic acid(Acetic acid)

CC OH CH3C OH

O O

Ester-oate

Methyl ethanoate(Methyl acetate)

CC O CH3C O

O OC CH3



Familyname



Amide-amide

Ethanamide(Acetamide)

CC NH CH3C NH2

O OCC NO

CC NH2

O

Carboxylicacid chloride

-oyl chlorideEthanoyl chloride(Acetyl chloride)

CC Cl CH3C Cl

O O

Carboxylicacid anhydride

-oic anhydrideEthanoic anhydride(Acetic anhydride)

CC O CH3C O

O OCO

C C CH3

O

Practice functional Groups


O O

O

O

HO

Coleophomone A


alkanes: saturated hydrocarbon, : aliphatic compound (meaning "fat")

3.2 Alkanes and Alkane Isomers

H3C CH3CH4CH3CH2CH3

Methane Ethane, C2H6 Propane, C3H8

general formula: CnH2n+2

Butane Isobutane(2-Methylpropane)

C4H10


Pentane 2-MethylbutaneC5H12

2,3-Dimethylpropane


- straight chain alkanes (normal alkane) - branched chain alkane

isomer: same formula but different structureconstitutional isomer: connected differently

Pentane 2-Methylbutane 2,3-Dimethylpropane

C5H12

Practice How many isomers ?


C6H14

5


- constitutional isomerism is not limited to alkanes

Butane Isobutane(2-Methylpropane)

Different carbon skeletonC4H10

Ethyl alcohol

Different functionalgroupC2H6O

CH3CH2OH

Diethyl ether

CH3OCH3

Ethyl alcohol

Different position offunctional groupC3H9N

CH3CHCH3

Propylamine

CH3CH2CH2NH2

NH2


CC

CC

H CH

HCH

HCH

HCH

HH

H

H H

H H

H HH

H H

H3C CH2 CH2 CH3 CH3CH2CH2CH3

CH3(CH2)2CH3

- different ways to represent n-butane (n= normal); n-C4H10

these structures do not imply any specific geometry


Names of straight chain alkanes: ending -ane

12345678

MethaneEthanePropaneButanePentaneHexaneHeptaneOctane

910111213202130

NonaneDecaneUndecaneDodecaneTridecaneIcosaneHenicosaneTriacotane


alkyl group: partial structure of alkane (-H); used for naming purpose

3.3 Alkyl Groups

CH4

Methane

H3C

A methyl group

H3C OH

Methyl alcohol

H3C NH2

Methyl amine

Methyl (Me)

-CH3

Ethyl (Et)

-CH2CH3

Propyl (Pr)

-CH2CH2CH3

Butyl (Bu)

-CH2CH2CH2CH3

Pentyl, or Amyl

-CH2CH2CH2CH2CH3


Propyl (n-Pr) Isopropyl (i-Pr)

n-Butyl (n-Bu) sec-Butyl (s-Bu)

Isobutyl (i-Bu) tert-Butyl (t-Bu)


four possible degrees of alkyl substitution for carbon

CH

HR H C

H

RR H

CR

RR H C

R

RR R

primary carbon (1o) secondary carbon (2o)

tertiary carbon (3o) quartenary carbon (4o)

R = a generalized alkyl groupAr = a generalized aryl group


CH

HR OH C

H

RR OH C

R

RR OH

primary alcohol (1o) secondary alcohol (2o) tertiary alcohol (3o)

CH3CH2CHCH3

CH3

a tertiary hydrogen

secondary hydrogens

primary hydrogens


IUPAC: International Union of Pure and Applied Chemistry

3.4 Naming Alkanes

ParentPrefix Suffix

What family?How many carbons?Where are the substituents?


Step 1. Find the parent hydrocarbon.

hexane heptane

a) the longest continuous chain of carbon atoms


two substituents one substituents

b) if two different chains of equal length are present; choose the one with the larger number of branch points


Step 2. Number the atoms in the main chain.

a) beginning at the end nearer the first branch point

heptane

1

2 34 5

6

7

7

6 44 3

2

1NOT


192

345

67

8

3,4,7

b) if there is branching an equal distance away from both ends; begin the end nearer the second branch point

918

765

43

2

3,6,7

NOT


Step 3. Identify and number the substituents.

192

345

67

8

a nonane

3-ethyl4-methyl7-methyl

a) assign a number to each substituent according to its point of attachment to the main chain


12

345

6

a hexane

2-methyl4-methyl4-ethyl

b) If there are two substituents on the same carbon, give them both the same number.


Step 4. Write the name as a single word.

3

- use hyphens to seperate the different prefixes- use comma to seperate numbers- cite in alphabetical order- more than one identical substituents; di-, tri-, tetra-...

(Don't use these prefixes for alphabetizing purposes)

192

345

67

8

3- Methylhexane

3-Ethyl-4,7-dimethylnonane


Me

Et2 3 3-Ethyl-2-methylheptane

4-Ethyl-3-methyloctane

4-Ethyl-2,4-dimethylheptane


Step 5. Name a complex substituent just as though it were itself a compound.

19

23

4 5 67

810

2,3,6-trisubstituted decane


Molecule1

2 3

- begin numbering at the point of attachment

2-methylpropyl group


The substituent is alphabetized according to the first letter of its complete name (including any numerical prefix) and is set off in parentheses.

19

23

4 5 67

810

2,3-Dimethyl-6-(2-methylpropyl)decane

6-Isobutyl-2,3-dimethyldecane


19

23

4 5 67

8

1

23

5-(1,2-Dimethylpropyl)-2-methylnonane

5-(1,2-dimethylpropyl)

- alphabetizing the substituent: the first letter of the complete name(including any numerical prefix of the complex substituent)

2-methyl

Practice IUPAC Name


6-(1-Ethylbutyl)-3,5-dimethylundecane

6-(1-ethylbutyl)

6


common names: historical reason

Isopropyl (i-Pr)

sec-Butyl (s-Bu) Isobutyl (i-Bu) tert-Butyl (t-Bu)

three-carbon alkyl group

four-carbon alkyl group


Isopentyl or isoamyl (i-amyl)

Neopentyl tert-Pentyl ortert-amyl (t-amyl)

five-carbon alkyl group


common name and IUPAC name, both are used

Cautioniso, neo, cyclo are considered part of the alkyl-group for alphabetizing purposes but sec-, tert- are not.

4-(1-Methylethyl)octane

or 4-Isopropyloctane

Practice IUPAC Name


27

2,7-Dimethylnonane

Practice IUPAC Name


3-Isopropyl-2-methylhexane

3 32


3.5 Properties of Alkanes

• alkanes are sometimes referred to as paraffins (meaning "slight affinity"); little chemical affinity for other substances; chemically inert to most laboratory reagents

combustion

CH4 + 2 O2 CO2 2 H2O+ + 890 kJ/mol (213 kcal/mol)

• alkanes do react with oxygen, chlorine, and a few other substances under appropriate conditions


photochemical chlorination

CH4 + +Cl2hν CH3Cl HCl

Cl2 +CH2Cl2 HCl

Cl2 +CHCl3 HCl

Cl2 +CCl4 HCl


• b.p. or m.p. of alkane increases with molecular weight due to intermolecular dispersion forces (van der Waals forces) between molecules.; C1 - C4 (gas): C5 ~ (liquid)


Dispersion forces (van der Waals forces) : operate only very small distances, arise because the electron distribution in alkane molecule, although uniform over the time, is likely to be nonuniform at any given instant. One side of a molecule may, by chance, have slightly excess of electrons relative to the opposite side, giving the molecule a temporary dipole moment. This temporary dipole in one molecule causes a nearby molecules to adopt a temporarily opposite dipole, with the result that a tiny electrical attraction is induced between the two. Temporary molecular dipoles have a fleeting existence and are constantly changing, but the cumulative effect of an enormous number of them produces attractive forces sufficient to cause a substance to remain in the liquid or solid state.

δ− δ+ δ− δ+ δ− δ+

attractive van der Waals force


3.6 Cycloalkanes• cycloalkanes or alicyclic compound

Cyclopropane Cyclobutane Cyclopentane

Cyclohexane Cycloheptane Cyclooctane

general formula: CnH2n

• b.p.of cycloalkane increases with molecular weight; but, m.p. is affected by molecular weight and shape


HH CO2H

Chrysanthemic acid

(insecticidal)

OH

OH

HOHHHO

O

H

Prostaglandin E1 (PGE1)

(hormone which controlsblood platelet aggregation,bronchial dilation,inhibition of gastric secretion)

O

OH

OOH

OH

HH

Cortisone


3.7 Naming Cycloalkanes

; if the number of carbons of ring ≥ the number of carbons in the substituent: name as cycloalkane

CH3

Step 1. Find the parent.

Methylcyclopentane

1-Cyclopropylbutane

; if the number of carbons of ring < the number of carbons in the substituent: name as alkane


; for alkyl- and halo-substituted cycloalkanes: choose a point of attachment as C1 and number others so that the second substituent has as low a number as possible

1

3

Step 2. Number the substituents.

1

5

1,3-Dimethylcyclohexane NOT


MeMe

Et

1

24

; if second point is same, choose lowest third or fourth

MeMe

Et1

26

2-Ethyl-1,4-dimethylcycloheptane

MeMe

Et

4

31

MeMe

Et

NOT


(a) When two or more different alkyl groups that could receive the same numbers of present, number them by alphabetical priority.

Me

Et1

2Me

Et

1

2

1-Ethyl-2-methylcyclopentane

NOT


(b) If halogens are present, treat them exactly like alkyl groups

Me

Br1

2Me

Br2

1

1-Bromo-2-methylcyclobutaneNOT

bromo > methyl

Practice IUPAC Name


1-Bromo-3-ethyl-5-methylcyclohexane

Br

Et Me

1

3 5

Br

Et Me

Practice IUPAC Name


(1-Methylpropyl)cyclobutane

1

sec-Butylcyclobutane

Practice IUPAC Name


1-Chloro-3-ethyl-2-methylcyclopentane

ClMe

Et

1

2

3

ClMe

Et


3.8 Cis-Trans Isomerism in Cycloalkanes

• In many respects, the chemistry of cycloalkanes is like that of open-chain, acyclic alkanes; nonpolar, inert.

• But cycloalkanes are less flexible than acyclic alkanes.; free rotation is possible around C-C bond in open-chain molecules (because σ-bond is cylindrically symmetrical)

H

CH H

H

HHC rotate

HC

H

HH

HHC


H

HH

H

H

H

No rotation is possible around the C-C bonds withoutbreaking open the ring

• cycloalkanes (C3-C7) are severely restricted in their molecular motions• larger cycloalkanes have increasingly more rotational freedom• very larger ring (C25 and up) are so floppy that they are nearly indistinguishable from open-chain alkanes.


• Cycloalkanes have two sides, a "top" side and a "bottom" side, leading to the possibility of isomerism in substituted cycloalkanes.

H3C

HH

CH3

H

HH3C

HH

H

CH3

H

trans-1,2-Dimethylcyclopropane

X

cis-1,2-Dimethylcyclopropane


stereoisomer: atoms connected in the same order but differ in 3-dimensional orientation

Constitutional isomers(different connections between atoms)

H3C

HH

CH3

H

HH3C

HH

H

CH3

H

trans-1,2-Dimethylcyclopropanecis-1,2-Dimethylcyclopropane

Stereoisomers(same connections but different 3-dimensional geometry)


• cis-trans isomer

HH

H3C CH3

cis

Br

H

H

Et

trans

HO

H

OH

H

cis

H3C

CH3HH

Br HH Et

HO

OH

Gasoline from PetroleumChemistry @ Work

natural gas and petroleum: derived from the decomposition of plant and animal matter, primarily marine origin

- natural gas : methane (major), ethane, propane, butane, isobutane

- petroleum : complex of hydrocarbons that must be refined into fractions before it can be used

refining by distillation of crude oil


Petroleum

Asphalt Lubricating oils,waxes

Heating oil(C14 - C25)

Kerosene(C11 - C14)

Straight-run gasoline(C5 - C11)

Natural gas(C1 - C4)


octane number: the measure by which its antiknock properties are judged

• straight-chain hydrocarbons are far more prone to induce engine knock than a highly branched compounds

CH3CH2CH2CH2CH2CH2CH3

Heptane(octane number = 0)

CCH3

CH3

CH2H3C CH

CH3CH3

Isooctane(octane number = 100)

bad fuel good fuel


• straight-run gasoline: a high percentage of unbranched alkanes, poor fuel

catalytic cracking: "cracking" high-boiling kerosene (C11-C14) into smaller molecules suitable for use in gasoline; on silica-alumina catalyst, 400-500 oC; major products are C3-C5 carbons which are then catalytically recombined to C7-C10 alkanes

3.1 Functional Groups - Yonsei University · 2017-11-13 · Ch.3 Organic Compounds: Alkanes and Cycloalkanes functional groups: a group of atoms within a molecule that has a characteristic

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