Structure and Functional Groups, Intermolecular Forces and Infrared (IR)

Spectroscopy

2.1-2.2 Hydrocarbons: RepresentativeCarbon-carbon formed the most strongest

bond in organic moleculesHydrocarbon: molecules that contain only H

& C

AlkanesPrinciple sources are natural gas and

petroleumSaturated hydrocarbons

No double or triple bondsGeneral formula: CnH2n+2

E.g CH4

C2H6

C3H8

Methane gasProduces carbon dioxide and hydrogen when

burning

Methane

AlkenesUnsaturated hydrocarbons: contain double

bonds

General formula: CnH2n

Used widely in the industry

Some occurs as plant hormoneInvolved in the ripening process

AlkenesStructure of ethene

AlkynesUnsaturated hydrocarbon with at least one

triple bondGeneral formula: CnH2n-2Use for biosynthesis

AlkynesEthyne

BenzeneSix membered ring with alternating single

bonds

resonance structure of benzene

Polar and NonPolar MoleculesDiatomic molecules with different polarity is

a polar molecules

Vectors cancelled out non polar

Dipole moment = charge (in esu) x distance (cm)

Must know 3-D structure

Cl

C

ClCl

Cl

vector sum = 0no net dipole momentnon polar molecule

Cl

C

HH

H

vector sum = 0 polar molecule

O

H H

Net Dipole momentPolar molecule

ExamplesUsing a three dimensional formula, show the

direction of the dipole moment of CH3OH. Write ∂- and ∂+ signs next to the appropriate atoms

Functional GroupsPart of a molecule where most of its chemical

reaction occur

Defined by characteristic arrangements of atoms

Determined the compound’s chemical properties

2.5 Alkyl and the symbol R# C N1ame Alkyl (one H has removed)

1 Methane Methyl

2 Ethane Ethyl

3 Propane Propyl

4 Butane Butyl

5 Pentane Pentyl

6 Hexane Hexyl

7 Heptane Heptyl

8 Octane Octyl

9 Nonane Nonyl

10 Decane Decyl

Functional groupsAlkyl groups are designated as RGeneral formula : R-H

CH3CHCH3

isopropyl

Phenyl and Benzyl groupsWhen benzene group is attached to some

other groups of atoms in molecule, it is called phenyl

Abbreviated as Ar

Ar

Phenyl and Benzyl groupsThe combination of a phenyl group and

methylene group ( -CH2-) is called benzyl group

BnH2C

2.6 Alkyl Halides or haloalkanesAlkyl halides are compounds in which a

halogen atom is replaced with a hydrogen atom from alkaneAlso known as haloalkanesGeneral formula: R-X

X = fluorine, chlorine, bromine and iodine

CH3Cl - chloromethane

Alkyl HalidesClassified as being

Primary (1o)Secondary (2o)Tertiary (3o)

R

H

H

X

1o alkyl halide

R

R

H

X

R

R

R

X

2o alkyl halide 2o alkyl halide

ExamplesWrite bond-line structure for

a. An alkane with formula C5H12 that has no secondary or tertiary carbon atoms

b. A secondary alkyl bromide with formula C4H9Br

c. Two constitutionally isomeric primary alky bromide

AlcoholsHydrocarbons that contain hydroxyl group

(OH)Attached to an sp3-hybridized carbon

O H

Functional group of an alcohol

AlcoholsClassified as

Primary (1o)Secondary (2o)Tertiary (3o)

R

H

H

OH

1o alcohol

R

R

H

OH

R

R

R

OH

2o alcoholor iso_

2o alcoholor tert_

ExamplesWrite bond-line structure formulas for

a. Two primary alcoholsb. A secondary alcoholsAll having the molecular formula C4H10O