Quick questions on Structural and geometric isomerism (QCE Chemistry Unit 4)

Structural isomers have the same molecular formula but different atom connectivity. There are three sub-types in the Unit 4 syllabus.

Stereoisomers have identical connectivity but different spatial arrangement. The Unit 4 syllabus covers cis-trans isomerism in alkenes.

For a question asking for "all isomers of C4H10O":

Same functional group and substituents, different carbon skeleton (branching).

Same carbon skeleton and same functional group, but the functional group sits at a different position.

Same molecular formula, different functional group (and different homologous series).

Cis isomers usually have a small net dipole; trans isomers are usually symmetrical and so non-polar. Cis tends to have slightly higher boiling point (dipole-dipole adds to dispersion) but lower melting point (less efficient crystal packing). The cis vs trans melting and boiling difference is a common QCAA stimulus.

Define structural isomers and give two structural isomers of $\text{C}_4 \text{H}_{10}$. [3 marks]

Identify the type of isomerism shown by cis- and trans-2-butene and state which has the lower boiling point. [3 marks]

Consider 2-bromobutane. (a) Identify the chiral centre. (b) Draw both enantiomers in 3-D.