Dictionary of Chemistry [6th Ed.]

4-hydroxybutanoic acid lactone

(γ-butyrolactone) A colourless liquid

*lactone, C 4 H 6 O 2 ; b.p. 206°C. It is

used as a solvent and in the produc-

tion of certain synthetic resins.

hydroxycerussite See lead(ii) car-

bonate hydroxide.

hydroxyethanoic acid See gly-

colic acid.

hydroxylamine A colourless solid,

NH 2 OH, m.p. 33°C. It explodes on

heating and may be employed as an

oxidizing agent or reducing agent. It

is made by the reduction of nitrates

or nitrites, and is used in making

nylon. With aldehydes and ketones it

forms *oximes.

A

• Information about IUPAC nomenclature
  hydroxylation The introduction of
  a hydroxyl group (–OH) into an or-
  ganic compound. For example,
  alkenes can be hydroxylated using
  potassium permanganate or lead
  ethanoate to give alcohols. In bio-
  chemistry, various enzymes can
  bring about hydroxylation.

hydroxyl group The group –OH in

a chemical compound.

2-hydroxypropanoic acid See lac-

tic acid.

hygroscopic Describing a sub-

stance that can take up water from

the atmosphere. See also deliques-

cence.

hyperconjugation The interaction

of sigma bonds with pi bonds in a

molecule, as in the interaction of a

methyl group with the benzene ring

in toluene. It is postulated to account

for the stability of some carbonium

ions. Hyperconjugation is often

thought of as a contribution of reso-

nance structures in which a sigma

bond is broken to give ions; e.g.

C 6 H 5 CH 2 – H+in toluene. It has been

called no-bond resonance.

hyperÜne structure See fine

structure.

hypertonic solutionA solution

that has a higher osmotic pressure

than some other solution. Compare

hypotonic solution.

hypochloriteSee chlorates.

hypochlorous acid See chloric(i)

acid.

hypophosphorus acidSee phos-

phinic acid.

hyposulphiteSee sulphinate.

hyposulphurous acid See sul-

phinic acid.

hypothesisSee laws, theories,

and hypotheses.

hypotonic solutionA solution

that has a lower osmotic pressure

than some other solution. Compare

hypertonic solution.

hypsochromic shift A shift of a

spectral band to shorter wavelengths

as a result of substitution in a mol-

ecule or as a result of a change in

the physical conditions. Compare

bathochromic shift.

4-hydroxybutanoic acid lactone 280

h