FUNCTIONAL GROUPS

FUNCTIONAL GROUPS

• A functional group is a cluster of atoms within a molecule that have specific reactivity patterns

• Compounds with the same functional group have similar physical properties

• The general formula for an organic compound with a functional group is R + functional group

• R stands for the alkyl group (carbon chain)

• If there is more than one alkyl group, we use R’, R’’

PHYSICAL PROPERTIES AND FORCES BETWEEN MOLECULES

• Physical properties are largely dictated by intermolecular forces

• There are three main types

• Hydrogen bonding strong intermolecular attraction between

• The H atom on a N-H, O-H, F-H group of one molecule and the N, O, or F of another molecule

• Dipole-Dipole interactions: between polar molar molecules

• Dispersion forces: between all covalent molecules

• Very weak for small molecules, but they strengthen as the size of the molecule get larger

SOME INTERESTING POINTS ABOUT INTERMOLECULAR FORCES

SINGLE-BONDED FUNCTIONAL GROUPS

1. ALCOHOLS

ALCOHOLS

PROPERTIES OF ALCOHOLS

2. ORGANIC HALIDES

PROPERTIES OF ORGANIC HALIDES

3. ETHERS

4. AMINES

PROPERTIES OF AMINES

PROPERTIES OF ETHERS

FUNCTIONAL GROPS WITH THE C=O BOND

THE CARBONYL GROUP

• Found in many compounds

• One of the most interesting functional groups

• The double bond makes it more reactive the a C-O single bond (in alcohols, ethers)

• Different reactivity patternsCH2

O

1. ALDEHYDES AND KETONES

• Hydrocarbons with a C=O functional group

• If the carbonyl group is at the end of the parent chain, it is an aldehyde

• If the carbonyl group is in the middle of the parent chain, it is an ketone

C

O

HR

C

O

HR

Terminal carbonyl group gives an aldehyde

General formula: R-CHO

C

O

RR

Internal carbonyl group gives a ketone

General formula: R-CO-R’

Examples

• Pentanal

• Aldehydes end in “–al”

C

O

HCH2

CH2CH2

CH3 C

O

CH2CH2

CH2CH2

CH3 CH2CH3

• 3-octanone

• Ketones end in “–one”

PROPERTIES OF ALDEHYDES AND KETONES

• The C=O is polar, so aldehydes and ketones are usually polar

• Hydrogen bonding cannot occur between molecules of these compounds

• But, since oxygen has two lone pairs, it can form weak hydrogen bonds with water

• The low molecule mass chains are soluble in polar solvents, as the number of carbons increase, the solubility decreases

• Boiling points are lower than analogous alochols

• i.e. Ethanol = 78.9°C; Ethanal = 20.2°C

• Propanol = 97°C; Propanone (acetone) = 56°C

• Odours:

• Aldehydes: strong pungent

• Ketones tend to smell sweet

• They are good organic solvents for both polar and non-polar compounds

• Acetone = propanone: one of the most common organic solvents in chemistry labs

• Remember: like-dissolves-like

• These are polar/non-polar at the same time, so they can dissolve both

2. CARBOXYLIC ACIDS

• The carboxyl group characterizes organic acids (proton donors)

• Recall: amines = organic bases

• These are always terminal, since they take up three of carbons four bonds

• General formula: R-COOH

• Names always end in –oic acid

• Example: pentanoic acid C

O

OHR

PROPERTIES OF CARBOXYLIC ACIDS

• Similar to alcohols

• Hydrogen bonding occurs between chains and with water molecules

• Melting and boiling points are higher than parent alkanes; increase with number of carboxyl groups

• Have unpleasant odours

• The H on the OH means that it can easily donate the H to another molecule

3. ESTERS

• Derivatives of carboxylic acids, where the ‘H’ of COOH has been replaced with an alkyl group

• Combination of carboxylic acid and alcohols

• Names in “-oate”

C

O

ORR

1

PROPERTIES OF ESTERS

• Usually polar molecules

• Do not have O-H bond, therefore do not form hydrogen bonds with each other

• Due to lone pairs on O atoms, can accept a hydrogen bon from water

• Low molecular masses are soluble in water and polar solvents

• Low boiling points, usually volatile liquids (combustible/explosive)

• Have pleasant odours and tastes

• Used as perfumes and artificial flavours

4. AMIDES

• Amides are derivatives of carboxylic acids, where the OH of the COOH has replaced with an amine group

• Combining a carboxylic acid and an amine

• Can be primary amides, secondary or tertiary

• Names end in: “amide”

C

O

NRR

1

R2

PROPERTIES OF AMIDES

• C-N, N-H, C=O bonds are polar, so molecules are usually polar

• Primary and secondary amides experience hydrogen bonding

• Soluble in water and other polar solvents, solubility decreases as the number of carbons increases

• Primary amides have higher melting and boiling points than analogous carboxylic acids

• Solid at room temperature

• Form the backbone of all proteins

Homework

• Practice Worksheet