Predicting Physical Properties of Molecules from Functional Groups

Learning outcomes To become familiar with identifying key functional groups within molecules. To be able to explain the influence of functional groups on intermolecular forces. To be able to predict the physical properties of molecules from functional groups present.

Butanoic acid has a powerful, unpleasant odour Butanoic acid has a powerful, unpleasant odour. It is found in rancid butter, Parmesan cheese and vomit. Carboxyl group Can you identify and name the functional group present in butanoic acid?

Can you identify and name the functional group present in methanal? Aqueous solutions of methanal are commonly used in embalming to preserve human or animal remains. Carbonyl group Can you identify and name the functional group present in methanal? Is methanal an aldehyde or a ketone? Aldehyde

Dettol (chloroxylenol) helps us fight unwanted bacteria. The molecule below is found in the disinfectant Dettol, which we instantly recognise by its distinctive smell. Dettol (chloroxylenol) helps us fight unwanted bacteria. Hydroxyl group Can you identify and name the functional group present in Dettol?

4-formamidobenzoic acid is used in pharmaceutical compositions. Carboxyl group Amide group Can you identify and name two functional groups present on the 4-formamidobenzoic acid molecule?

Can you identify and name two functional groups in cinnamon? Cinnamon is a tasty spice used to flavour biscuits, cakes and pies. Cinnamon also has medicinal properties. Carbonyl group Carbon-to-carbon double bond Can you identify and name two functional groups in cinnamon? Is cinnamon an aldehyde or a ketone? Aldehyde

What is the strongest type of intermolecular force of attraction between cinnamon molecules? (Hint: Think about the bond polarity of the functional groups present!) Permanent dipolepermanent dipole interactions between polar carbonyl groups are the strongest intermolecular force of attraction.

Methyl anthranilate occurs naturally in grapes and is used as grape flavouring in drinks and chewing gum. Ester link Amino group Can you identify and name the two functional groups present in methyl anthranilate?

Vitamin C is needed in your diet for the growth and repair of tissues in all parts of your body. Ester link Carbon-to-carbon double bond Hydroxyl group Can you identify and name three different types of functional group on the structure of vitamin C?

Which is the strongest type of intermolecular force of attraction between molecules of vitamin C? Hydrogen bonding between the highly polar OH groups.

Is vitamin C a polar or a non-polar molecule? Is vitamin C soluble in water or in hexane? (Hint: Think about which functional groups are present!) Vitamin C is a polar molecule because of the presence of four hydroxyl groups. Hydroxyl groups are highly polar because of the large difference in electronegativity between the hydrogen and oxygen atoms in the bond. Hydrogen bonding therefore exists between vitamin C molecules. Students should understand that ‘like dissolves like’ so polar molecules dissolve in polar/ionic solvents. Vitamin C is soluble in water (a polar solvent) not in hexane (a non-polar solvent).

Glucose is a simple sugar that is used as an energy source by many living organisms. Glucose is water soluble as it contains many polar hydroxyl groups. Water is a polar solvent. Is glucose soluble in water or in hexane? Justify your answer with reference to the functional groups present.

2-methylpropane is a branched hydrocarbon that is used as a refrigerant. 2-methylpropane is soluble in hexane since it is non-polar molecule and hexane is a non-polar solvent. Is 2-methylpropane soluble in water or in hexane? Justify your answer with reference to the structure.