2.2 nomenclature and isomerism in organic compounds

Homologous series

Same general formula

Similar chemical properties

Successive members differ by CH2

Alkanes General formula, functional group example

CnH2n+2 -ane

C-H e.g ethane C2H6

Alkenes General formula, functional group example

CnH2n

-ene C= C e.g ethene C

Alchoho’s General formula, functional group example

CnH2n+1OH

-ol , hydroxyl-

-OH E.g ethanol or hydroxyethane CH3CH2OH

Carboxylic acid General formula, functional group example

CnH2n+1COOH

oic acid H-C=O

E.g ethanoic acid CH3COOH

Haloalkanes , functional group example

Halo- -

Cl - Br - I

e.g chloroethane CH3CH2Cl

Aldehydes functional group example

-al. - H-C=O

E.G ethanal CH3COH3

Ketones functional group example

-one C=O

E.g propanone CH3COCH3

1-10 prefix’s

1- Meth. My

2. Eth- Evil

3. Prop- parents

4. But- buy

5. Pent- parents

6. Hex- horribly

7. Hept-

8. Oct-

9. Non-

10. Dec-

Molecular formula definition

The actual number of atoms of each element in a molecules

E.g ethane C2H6, ethanol C2H6O, ethanoic acid C2H3O2

Structural formula def

Shows all atoms and covalent bonds

Condensed structural formula

- arrangement of atoms and groups at each carbon atom, (brackets if two different groups attached.

Empirical formula

The simplest ratio of the atoms of the different elements in an organic compound

E.g ethanoic acid CH3COOH - CH2O

Skeletal formula

Carbon structure zig zag - omitting hydrogen atoms

Rules naming compounds

1. longest continuous carbon chain prefix

2. No methyl groups on end or start of chain

3. C atoms number in lowest number possible

4. Two substituent given prefix- di-, tri-, tetra-

5. Tw diff substituents given in alphabetical order e.g 2,4- dichloro-3-methylpentane

Substituent group names

-CH3- methyl, C2H5- ethyl, C37 propyl, C4H9 butyl

-F Fluor CL chloro, -Br broom, I- Iodo

Isomer definition

Isomers are molecules with the same molecular formula but different arrangement of atoms

Structural isomerism definition

Molecules which have the same molecular formula but a different structural formula

Chain isomerism

Same molecular formula - diff arrangement of atoms in carbon chain e.g butane , 2-methylpropne

E.g C5H12 pentane, 2-methylbutane, 2,2-dimethylpropane

Position isomerism

Isomers compounds in which same functional group but different arrangement positions in carbon chain

Propan-1-ol propan-2-ol

Functional group isomerism definition

Molecules same molecular formula but different functional group

Functional group isomerism Aldehydes and ketones

Aldehydes - func group at end

Ketones - func in middle

Functional group isomerism carboxylic acids and esters

What are stereoisomerism

Molecules which have the same molecular and structural formula but different 3D spatial arrangements.

Geometric isomerism

Geometric isomerism - compounds have the same structural formula but different arrangements of atoms due to the presence of one or more C=C bonds.

What causes geometric isomerism

C=C bond energy barrier to free rotation so restricted rotation around carbon carbon double bonds

Why does 3-methylpent-2-ene exists as geometric isomerism,

1. Restricted rotation around C=C

2. Both carbons in C=C have 2 different atoms/groups attached

Two types of geometric. Isomerism

Cis-trans isomerism

E-Z isomerism

When is cis-trans notation used.

Both carbons of C=C bonds have hydrogen atom and non-hydrogen atoms directly attached to them

Cisn and trans isomers. definitions

CIS - HYDROGEN SAME SIDE. OF C=C

TRANS- HYDROGEN OPPOSITE-SIDES OF C=C

E-Z isomerism

Assigning priority , both substituents of higher. Priority same side = Z while opposite is E

Assign- atomic number higher priority, next atom or sequence of atoms in subsequent group