rocket propellant. The name comes
from ‘High Molecular Weight RDX’.
HNIW(hexanitrohexaazaisowurtzi-
tane)A powerful explosive, C 6 N 12 O 12.
It has a three-dimensional bridged
structure containing six N–NO 2
groups. Also known as CL20, it is
extremely sensitive and so far has
not been produced in bulk.HNIW 272h
NN
N NN N
O NO 2
2 NO 2 NO 2 N NO 2NO 2HNIWHoff, Jacobus Henrikus van’t
(1852–1911) Dutch physical chemist
whoÜrst recognized that a molecule
could exist in two mirror-image
forms. He proposed that these forms
rotated the plane of polarization in
opposite senses, and is generally re-
garded as the founder of stereochem-
istry. Van’t Hoff also did important
work on other branches of physical
chemistry, especially chemical ther-
modynamics. He was awarded the
1901 Nobel Prize for chemistry.Hofmann’s reaction (Hofmann re-
arrangement)A reaction for making
primary *amines from *amines
using bromine or chlorine and
sodium hydroxide:
RCONH 2 →RNH 2
The halogen replaces a hydrogen
atom from the amido group to form
a halo-amide. This then reacts with
the alkali to produce an isocyanate,
which decomposes into the amine
and carbon dioxide. The amine has
one carbon atom fewer than the
amide from which it is produced.
This technique is used to reduce the
length of carbon chains in moles-cules (the Hofmann degradation).
The reaction is named after the Ger-
man chemist August Wilhelm von
Hofmann (1818–92).
hole1.A vacant electron position
in the lattice structure of a solid that
behaves like a mobile positive
*charge carrier. 2.A vacant electron
position in one of the inner orbitals
of an atom.
holmiumSymbol Ho. A soft silvery
metallic element belonging to the
*lanthanoids; a.n. 67; r.a.m. 164.93;
r.d. 8.795 (20°C); m.p. 1474°C; b.p.
2695 °C. It occurs in apatite, xeno-
time, and some other rare-earth min-
erals. There is one natural isotope,
holmium–165; eighteen artiÜcial iso-
topes have been produced. There are
no uses for the element, which was
discovered by Per Cleve (1840–1905)
and J. L. Soret in 1879.
A- Information from the WebElements site
holohedral formThe form of a
crystal in which the full number of
faces required for the symmetry are
present. Compare holohedral form.
HOMOSee highest occupied mo-
lecular orbital.
homocyclicSee cyclic.homogeneousRelating to only
one phase, e.g. a homogeneous mix-
ture, a homogeneous *catalyst. Com-
pare hetereogeneous.
homoleptic compoundA chemi-
cal complex with only one type of
ligand, as in nickel carbonyl or lead
tetraethyl.homologous seriesA series of re-
lated chemical compounds that have
the same functional group(s) but dif-
fer in formula by aÜxed group of
atoms. For instance, the simple car-
boxylic acids: methanoic (HCOOH),
ethanoic (CH 3 COOH), propanoic