Organic Chemistry: Test Review

Key facts

Where marks get lost

• ×Using the chain as it is drawn instead of the longest continuous chain, which produces impossible names such as 2-ethylbutane (really 3-methylpentane) or 1-methylbutane (really pentane). (Hydrocarbons: Naming and Isomers)
• ×Numbering an alkene to give the branch the lowest number instead of the double bond, e.g. calling $\mathrm{C}{\mathrm{H}}_2=\mathrm{CHCH}(\mathrm{C}{\mathrm{H}}_3)\mathrm{C}{\mathrm{H}}_3$ 2-methylbut-3-ene instead of 3-methylbut-1-ene. (Hydrocarbons: Naming and Isomers)
• ×Alphabetizing by the di- or tri- prefix, writing 2,2-dimethyl-3-ethylpentane instead of 3-ethyl-2,2-dimethylpentane. (Hydrocarbons: Naming and Isomers)
• ×Claiming cis-trans isomers for propene or but-1-ene, where one double-bond carbon carries two identical H atoms. (Hydrocarbons: Naming and Isomers)
• ×Treating benzene as if it had three ordinary double bonds that react like an alkene; its delocalized electrons make it much less reactive. (Hydrocarbons: Naming and Isomers)
• ×Confusing ethers and esters: an ester has a C=O next to the single-bonded O (–COO–), and an ether has no C=O at all. (Functional Groups and Their Properties)
• ×Naming an ester backwards: in $\mathrm{C}{\mathrm{H}}_3\mathrm{COOC}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$ the ethyl group is on the O, so the name is ethyl ethanoate, not methyl propanoate (which is a different isomer). (Functional Groups and Their Properties)
• ×Forgetting that the C=O carbon counts in the chain, calling $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{COOH}$ "ethanoic acid" instead of propanoic acid. (Functional Groups and Their Properties)
• ×Assuming every polar molecule hydrogen bonds: propanone and ethers have O atoms but no O–H, so they cannot hydrogen bond with each other. (Functional Groups and Their Properties)
• ×Writing a locant for an aldehyde (butan-1-al) but leaving one out for a ketone where it matters (pentanone could mean pentan-2-one or pentan-3-one). (Functional Groups and Their Properties)
• ×Calling a carbon chiral because it has four groups attached. Every saturated carbon has four groups; they must all be different. (Stereoisomers and Chirality)
• ×Comparing only the first atom of each group. –$\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$ and –$\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$ both start with $\mathrm{C}{\mathrm{H}}_2$ but are different groups; compare the whole group. (Stereoisomers and Chirality)
• ×Expecting enantiomers to have different boiling points. They have identical physical properties; only optical rotation and interactions with chiral substances differ. (Stereoisomers and Chirality)
• ×Thinking a racemic mixture is optically inactive because it contains no chiral molecules. It contains equal amounts of both enantiomers, whose rotations cancel. (Stereoisomers and Chirality)
• ×Confusing cis-trans isomers with enantiomers. Cis-trans isomers are not mirror images and have different physical properties; enantiomers are mirror images with identical ones. (Stereoisomers and Chirality)
• ×Putting the H on the wrong carbon when HBr or water adds to an unsymmetrical alkene, e.g. giving 1-bromopropane as the main product from propene instead of 2-bromopropane. (Organic Reactions)
• ×Oxidizing a secondary alcohol to an aldehyde or acid, or claiming a tertiary alcohol oxidizes; count the H atoms on the carbon bearing the –OH. (Organic Reactions)
• ×Leaving water out of an esterification or hydrolysis equation, so the atoms do not balance. (Organic Reactions)
• ×Calling a reaction with two products an addition: an addition to an alkene gives one product, while a substitution always gives two. (Organic Reactions)
• ×Expecting benzene to add bromine like an alkene; it keeps its ring and undergoes substitution instead. (Organic Reactions)
• ×Leaving the C=C in the repeating unit of an addition polymer: the double bond is used up making the chain, so the backbone has only single bonds. (Polymers and Organic Compounds in Society)
• ×Saying addition polymerization releases water, or forgetting the water released at every link in a condensation polymer. (Polymers and Organic Compounds in Society)
• ×Choosing a monomer with only one functional group (such as ethanol) for a condensation polymer; each monomer needs two reactive groups so the chain can keep growing. (Polymers and Organic Compounds in Society)
• ×Assuming a resin code means an item is recyclable everywhere, or that a "biodegradable" plastic will break down in a landfill. (Polymers and Organic Compounds in Society)
• ×Treating a small amount of a volatile solvent as harmless: its vapour can reach a distant flame, and pouring it down a sink harms water systems. (Polymers and Organic Compounds in Society)
• ×Calling aspirin synthesis a neutralization because an acid is involved. The phenol –OH of salicylic acid forms an ester: it is esterification (a condensation-type reaction). (Organic Compounds in Everyday Life: Risks, Benefits and Choices)
• ×Saying hydrogenation is a substitution. ${\mathrm{H}}_2$ adds across the C=C, so it is an addition reaction and the product has two more H atoms per double bond. (Organic Compounds in Everyday Life: Risks, Benefits and Choices)
• ×Thinking trans fats come from frying in general. They mainly come from partial hydrogenation, when some cis double bonds isomerize to trans on the catalyst. (Organic Compounds in Everyday Life: Risks, Benefits and Choices)
• ×Assuming any compound with an –OH group is water-soluble. Vitamin A and vitamin D each have an –OH, but their large hydrocarbon parts make them fat-soluble. (Organic Compounds in Everyday Life: Risks, Benefits and Choices)
• ×Saying soap does not work in hard water because it cannot dissolve. Soap dissolves, but its carboxylate ions react with $\mathrm{C}{\mathrm{a}}^{2+}$ and $\mathrm{M}{\mathrm{g}}^{2+}$ to form an insoluble precipitate (scum). (Organic Compounds in Everyday Life: Risks, Benefits and Choices)

Practice test

24 questions from across the unit. Each one shows the lesson it comes from.

Endless drill

Fresh numbers every time, for the calculation questions in this unit.