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 patterns

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

Terminal carbonyl group gives an aldehyde General formula: R-CHO Internal carbonyl group gives a ketone General formula: R-CO-R’

Examples Pentanal Aldehydes end in “–al” 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

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”

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”

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

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