Identifying Functional Groups In Organic Chemistry Quiz

Alkenes, also called olefins, are molecules containing a carbon-carbon double bond. The simplest alkenes, with only one of these double bonds and no other functional groups, have the general formula C(n)H(2n), i.e. for every carbon molecule, it has two hydrogen molecules. However, they can also be cyclic (containing a ring) and/or contain multiple carbon-carbon double bonds. An alkene molecule with one hydrogen atom removed is termed an alkenyl group and can form part of a larger molecule with other functional groups present. Larger alkenes can form isomers, where the molecule has the same total of C and H atoms but a different geometric configuration. The alkene in the picture is specifically a cis-alkene (from Latin meaning "on the same side"), where the R groups are both on the same side of the carbon-carbon double bond. In contrast, a trans-alkene (from Latin meaning "on the other side") has two R groups on opposite sides of the double bond. Some alkenes have four different R groups connected to the double bond; these are called tetrasubstituted alkenes.

Alkenes are planar non-polar molecules that dissolve in organic solvents but not water. The presence of the double bond means they are unsaturated and can undergo addition reactions, e.g. hydrogenation, which adds hydrogen atoms across the double bond, changing it to a single bond: this transforms an alkene into the corresponding alkane, e.g. propene (C3H6) + hydrogen (H2) --> propane (C3H8), and requires a catalyst. Other molecules can be incorporated into an alkene this way, e.g. using water to transform an alkene into a corresponding alcohol, or using halogens. A common use of alkenes is in the production of plastics, for example, polythene (also called polyethylene) which is a polymer of ethene (also called ethylene).

The characteristic of an alcohol molecule is a hydroxyl (-OH) group. Their general formula is R-OH. The term "alcohol" in common use usually refers to ethanol (C2H5OH) but there are many different types of alcohol molecules, whose names often end in "-ol", e.g. methanol (CH3OH) or propanol (C3H7OH). The molecule in the photo is termed a tertiary alcohol, i.e. one where the carbon beside the -OH group is bonded to three other carbon molecules (part of the R groups). Primary and secondary alcohols are those in which this carbon is bonded to one other or two other carbon atoms respectively.

Although the simplest alcohols may differ from the corresponding alkane by no more than the presence of an oxygen atom, i.e. an -OH group instead of an -H, this hydroxyl group generally makes alcohol molecules polar, which makes them more soluble in water than hydrocarbons like alkanes or alkenes, although larger alcohols are less soluble in water than smaller ones. Primary and secondary alcohols can be oxidised to form aldehydes and ketones respectively; ethanol in the alcoholic drinks we imbibe is partially oxidised to acetaldehyde by the liver and this compound plays a role in causing the dreaded hangover. Alcohols can be used as fuels, solvents, and for disinfecting (e.g. rubbing alcohol, which is a secondary alcohol also called isopropyl alcohol).

Ketones have the general formula R-C(=O)-R. Like other groups of organic compounds such as carboxylic acids or esters, they contain the carbonyl group (a carbon-oxygen double bond). Their structure is very similar to the corresponding aldehyde, whose carbonyl group is located on a carbon at the end of the chain (R-C(=O)-H) instead of in the middle of the chain as in ketones. The names of aldehydes generally end in -al while those of ketones end in -one, although many of these molecules also have common names. Aldehydes and ketones are polar molecules although their solubility in water decreases as the molecules get larger. One of the biggest differences between aldehydes and ketones is that aldehydes are much more readily oxidised into carboxylic acids. This property can be used to distinguish aldehydes from ketones, e.g. with Tollens' reagent.

Various aldehydes and ketones are well known. For example, formaldehyde (methanal), the simplest aldehyde, is produced industrially by oxidising methanol and is known for its use to preserve tissues, although due to it being a carcinogen, this use has decreased more recently. Acetone (2-propanone) is well-known as a household solvent and is also used industrially. Aldehydes and ketones are used in the production of plastics. Diabetic ketoacidosis is a dangerous complication of diabetes in which ketones build up in the blood due to a lack of insulin; the person's breath is often said to smell fruity or like nail polish remover due to the presence of acetone.

Amines are compounds where the hydrogen atoms of ammonia are replaced with R groups: when 1, 2, or 3 of these are replaced, then the amine is said to be primary, secondary, or tertiary respectively. Their general formulae are: R-NH2 (primary), R2-NH (secondary), and R3-N (tertiary). The amine in the picture is a primary amine. All amines can form hydrogen bonds with water and amines that are gases at room temperature are often sold as a solution in water. Amines are basic (as opposed to acidic) molecules and generally smell like ammonia, with the smell tending to get fishier or more like rotting meat as the molecules get larger. Trimethylaminuria, a genetic disorder that causes problems with metabolising trimethylamine, causes a person's sweat, breath, and urine to have a fishy smell.

As suggested by their name, amino acids are molecules that contain both amine and acid groups (mainly carboxylic acid). Amine hormones are synthesised in the body from the amino acids tryptophan and tyrosine, and include thyroid hormones as well as adrenaline and dopamine, which are also neurotransmitters. Industrial uses of amines include tanning leather, producing dyes and pharmaceutical drugs.

A nitrile compound contains a carbon-nitrogen triple bond. The term "nitrile" is generally used for organic compounds containing this group and "cyano" for inorganic compounds, although some sources will use the terms interchangeably. (Confusingly, the carbon atoms in the same molecule are counted differently with each name; with "nitrile" the carbon in the C≡N is counted in the carbon chain while for "cyanide" it is not: e.g. propionitrile is the same compound as ethyl cyanide.) Nitriles are polar molecules with high boiling points when compared generally to other molecules of a similar size, and, like other organic polar compounds, the smaller ones are soluble in water but this solubility decreases as the molecules get larger.

Nitrile is used to make nitrile rubber, commonly used for disposable gloves used in laboratories, hospitals, etc., and it is also used in the transport industry, such as in self-sealing fuel tanks, O-rings, gaskets, etc. The two main methods of industrial production of nitriles are the ammoxidation (using oxygen and ammonia) and hydrocyanation (using hydrogen cyanide) of alkenes. Nitriles also occur naturally in plants and animals, and pharmaceutical drugs containing nitrile groups have been developed.

Carboxylic acids have a general formula of R-C(=O)-OH. They are generally weak acids, i.e. they only partially ionise when dissolved in a solvent. Carboxylic acids widely occur in nature and are also produced industrially. Protein synthesis includes the formation of peptides, where multiple amino acids are linked together by the reaction of the carboxyl group of one amino acid with the amino group of another, forming peptide bonds. A common carboxylic acid is ethanoic acid (or acetic acid), also known as vinegar. Fatty acids contain carboxylic acid groups and occur in various foodstuffs, animal and vegetable fats, soaps, etc.

Carboxylic acids can undergo reactions to form various derivatives, including esters, which generally smell sweeter and more pleasant than sour-smelling carboxylic acids and are used in the perfume industry. Carboxylic acids are also used in the production of polymers, pharmaceutical compounds, and additives to food such as citric acid, which is used as a flavour enhancer and preservative.

The characteristic feature of ethers is an oxygen atom bonded to two separate carbon atoms, i.e. C-O-C. However, other molecules do contain this fragment but are not considered ethers, e.g. esters. The general formula of an ether is R-O-R. When the two R groups are the same, the ether is said to be symmetrical, and if they are not, unsymmetrical. Ethers are weakly polar, and while they are soluble in organic solvents, solubility in water decreases as the molecules get larger. Their boiling points are comparable to alkanes of a similar size.

Although they are fairly unreactive, ethers should be kept in tightly sealed containers unexposed to air, as they can undergo autoxidation, which is the slow oxidation over time of compounds exposed to air, and be transformed into potentially explosive peroxides. Due to their being relatively unreactive, ethers are frequently used as solvents. The compound commonly called "ether" is diethyl ether, and as well as its use as a solvent, it is used as a fuel additive and was previously widely used as a general anaesthetic.

The general formula of esters is R1-C(=O)-O-R2. They are essentially a carboxylic acid with the hydrogen atom of the -C(=O)-O-H replaced by an R group. They can be produced by reacting carboxylic acids with alcohols; e.g. butanoic (also butyric) acid plus methanol produces methyl butanoate (CH3-CH2-CH2-C(=O)-O-CH3), i.e. butanoic acid loses its H from the carboxyl group and joins with the methyl group (CH3) from the methanol, which has also lost its -OH: this -H and -OH form water as a by-product of the reaction. This is a reversible reaction: in the opposite direction, the ester can be hydrolysed into the carboxylic acid (or carboxylate ion) and an alcohol. When this is done with an alkaline solution, it is called saponification and is the process of forming soap from the glycerides in animal and vegetable fats and oils. This turns the glycerides into fatty acid salts and glycerol. The glycerol can be left in the soap or removed with salt.

Esters are known for their aromas and flavours; for example, octyl acetate is an ester found in citrus fruits. This property means that esters are widely used in the production of perfumes, cosmetics, flavourings, etc. Pheromones also contain esters. Polyesters are polymers of esters used to make clothing and other materials while nitrate esters (including nitroglycerin) are used as explosives.

Not to be confused with the similarly named "amine" group, an amide group contains a carbon-oxygen double bond connected to a nitrogen atom. It can be thought of as a combination of a carboxylic acid and an amine. Like many other organic molecules, amides can be primary, secondary, or tertiary: a key difference here is that this refers to the groups bonded to the nitrogen atom, not the carbon atom. The amide in the picture is a primary amide, as the nitrogen is bonded to one non-hydrogen group. Secondary and tertiary amides are those in which the N atom bonds to two and three non-hydrogen groups respectively.

With high melting and boiling points, most simple amides are solid at standard temperature and pressure; the exception, formamide (also called methanamide), HC(=O)NH2, is liquid. They are polar molecules and smaller ones are soluble in water. Protein synthesis from multiple amino acids involves the formation of amide bonds (also called peptide bonds) by the reaction of the carboxyl group of one amino acid with the amine group of another. Amides are also used in industry, such as in the synthesis of dye and as organic solvents. Polyacrylamides are used in the treatment of water and making paper.

The general formula for a thiol is R-S-H, and indeed the name derives from the Ancient Greek for sulfur, "theion". The "-ol" part derives from the fact that thiols are sulfur analogues of alcohol, i.e. the oxygen atom in the -OH group of an alcohol is replaced by a sulfur atom in thiols. Thiols react very strongly with mercury-containing compounds and therefore are also sometimes called "mercaptans", from Latin "mercurio captans" ("capturing mercury"). One of the proteinogenic amino acids, cysteine, contains a thiol group. Two cysteine residues near each other in a protein can form a strong disulfide bond between each of their sulfur atoms, which affects the folding structure of the protein.

Perhaps the most prominent characteristic of thiols is their odour, which can be like strong onion or garlic, or in the case of low-weight thiols, skunk spray (indeed, these are actually in skunk spray!). Volatile thiols are added as an odorant to odourless gas to help detection of gas leaks. Sulfides (also called thioethers) are the sulfur analogues of ethers: their general formula is R-S-R. The other sulfur-containing proteinogenic amino acid, methionine, contains a thioether group. It has less of an effect on the protein than the sulfur atoms in cysteine.