Describe the Cross-aldol condensation.

Which acid of each pair shown here would you expect to be stronger? (i) ${\mathrm{CH}}_3\mathrm{COOH}$ or ${\mathrm{CH}}_2\mathrm{FCOOH}$

Give the structure of the following:

Phthalaldehyde

Give the structure of the following:

$3$-Methylcyclohexanecarbaldehyde
 

Give the structure of the following:

 $3$-methylbut-$2$-enoic acid