heterovalent hyperconjugation See HYPERCONJU-
GATION.
Heyrovsky, Jaroslav (1890–1967) Czechoslovakian
Electrochemist Jaroslav Heyrovsky was born in
Prague on December 20, 1890, the son of Leopold
Heyrovsky, professor of Roman law at the Czech Uni-
versity of Prague, and his wife Clara (née Hanl). He
went to secondary school until 1909, when he began
studying at the Czech University, Prague, in the fields
of chemistry, physics, and mathematics. He continued
his studies at University College, London, from 1910 to
1914, receiving a B.Sc. in 1913. He received a Ph.D.
degree in Prague in 1918, and a D.Sc. in London in
1921 and started his university career as assistant to
Professor B. Brauner in the Institute of Analytical
Chemistry of the Charles University, Prague. He later
was promoted to associate professor in 1922, and four
years later became the first professor of physical chem-
istry at this university.
In 1922 he invented the polarographic method in
electrochemistry (polarography is based on electro-
lysis using a dropping mercury electrode), and he
continued development of this new branch of electro-
chemistry for decades. In 1926 he married Marie
Koranová and had two children. In 1950 he was
appointed director of the newly established Polaro-
graphic Institute (incorporated into the Czechoslovak
Academy of Sciences in 1952). In 1959 he was
awarded the Nobel Prize in chemistry “for his discov-
ery and development of the polarographic methods of
analysis.”
He was a member of most of the leading scientific
organizations and had honorary doctorates from many
international universities. He died on March 27, 1967,
in Prague, Czechoslovakia.
hidden return SeeION-PAIR RETURN.
high-density polyethylene(HDPE) Polyethylene is
a plastic polymer composed of carbon and hydrogen
atoms with the formula –(CH 2 –CH 2 )n– made by poly-
merizing ethylene. In the high-density form, the poly-
mer chains are unbranched (linear), producing a
material of improved strength.
highest occupied molecular orbital(HOMO) The
highest-energy molecular orbital of an atom or
molecule containing an electron. Most likely the first
orbital, from which an atom will lose an electron.high-performance liquid chromatography(HPLC)
An analytical technique for the separation and determi-
nation of solutes in any sample (such as biological,
pharmaceutical, environmental, etc.). During the pro-
cess, a liquid (the eluant) is pumped (usually at high
pressure) through a porous, solid, stationary phase,
which separates the solute species, and then into a
flow-through detector.high spin SeeLOW SPIN.high-temperature superconductor Four classes of
superconductors that have been discovered since 1986
have much higher transition temperatures than previ-
ously known superconductors. These resistance-free
conductors are made of ceramic materials that exhibit
superconducting properties at temperatures from 20 to
130 K (–423 to –225°F) and require less-expensive
cooling systems than those needed for low-temperature
superconductors (<10 K, –441°F).Hildebrand parameter A parameter measuring the
cohesion of a solvent (energy required to create a cavity
in the solvent).Hill, Archibald Vivian(1886–1977) BritishPhysiol-
ogist Archibald Vivian Hill was born in Bristol on
September 26, 1886. After an early education at Blun-
dell’s School, Tiverton, he entered Trinity College,
Cambridge, with scholarships. He studied mathematics
but was urged to go into physiology by one of his
teachers, Walter Morley Fletcher.
In 1909 he began to study the nature of muscular
contraction and the dependence of heat production on
the length of muscle fiber. During the years 1911–14
until the start of World War I, he continued his work
on the physiology of muscular contraction at Cam-
bridge as well as on other studies of nerve impulse,
hemoglobin, and calorimetry.128 heterovalent hyperconjugation