O
CTOBER
2002 T
ODAY
’
S
C
HEMIST AT
W
ORK
51
©2002 A
MERICAN
C
HEMICAL
S
OCIETY
PH
O
TO COURTES
Y OF RO
ALD H
OFFMANN
I
n high school, chemistry was not
one of Kenichi Fukui’s favorite subjects.
He loved mathematics, and was also
considered a literary scholar, known for his
great love of books and languages. But in
1981, Fukui became the first Japanese
scientist to receive the Nobel Prize in Chem-
istry, for his frontier orbital theory of chem-
ical reactivity. Based on his research on
the specific properties of electronic orbitals,
Fukui’s theory transformed scien-
tists’ ability to predict the routes
and products of chemical reactions.
Born in Nara, Japan, in 1918,
Fukui was the eldest of three sons
born to Ryokichi and Chie Fukui.
His father, Ryokichi, was a foreign
trade merchant and factory manag-
er. Although he was not enam-
ored of chemistry, Fukui took the
advice of a respected professor and
entered the Department of Indus-
trial Chemistry at Kyoto Universi-
ty, thus beginning a lifelong affil-
iation with the school. After
obtaining a B.A. in engineering in
1941, he accepted a position with
the Japanese Army Fuel Laboratory, where
he participated in Japan’s World War II
effort by developing synthetic fuels. He
returned to Kyoto University in 1943 and
became a lecturer in the Fuel Chemistry
Department.
Simultaneously, he began work on his
doctoral degree. Rising through the academ-
ic ranks, he became an assistant professor
in 1945, received his Ph.D. in chemical
engineering in 1948, and achieved the rank
of full professor in 1951.
Although Fukui was trained as an engi-
neer and had done applied fuel research,
he developed an interest in quantum chem-
istry. He became a largely self-taught theo-
retician and actively pursued this interest
soon after returning to Kyoto University.
By 1956, Fukui had gathered around him
a group of experimentalists and theoreti-
cians who went on to produce more than
450 papers over the next 30 years, among
which were some that dealt with the
electronic theory of organic reactions. Other
papers were about the statistical theory of
gelation, organic synthesis by inorganic
salts, and polymerization kinetics and cata-
lysts. Fukui also continued to work in exper-
imental organic chemistry and published
137 papers on the subject between 1944
and 1972.
“Delightful Discovery”
In 1952, Fukui published the first paper
detailing his theoretical work on the rela-
tionship between molecular orbitals (MO)
and chemical reactivity. He had found a
correlation between the frontier electron
density and the chemical reactivity in
aromatic hydrocarbons (he referred to this
as a “delightful discovery”). This paper
provided a simplified theoretical basis for
American Nobel Laureate Robert Mulliken’s
findings on charge transfer and electron
donor acceptors in complex chemical struc-
tures. Fukui believed that a reaction should
occur at the position of largest electron
density in the frontier (highest occupied
or lowest unoccupied) orbitals. Because
many experimental chemists at that time
did not have the necessary mathematical
background to understand its potential,
and because many theoretical chemists
thought the idea too simplistic, the paper
was largely ignored.
Undeterred, Fukui and his colleagues
continued to broaden their theories and
experiments and published two more impor-
tant papers in 1954. In the first of these
papers, Fukui included nucleophilic and
free-radical attack on conjugated hydro-
carbons in his methods. He showed that
these could be correlated respectively with
the substrate position having the great-
est virtual electron density—the lowest
unoccupied molecular orbital (which was
later called LUMO).
In the mid-1960s, Fukui and
Roald Hoffmann (a Polish-born
American chemist) discovered—
almost simultaneously and inde-
pendently of each other—that
symmetry properties of frontier
orbitals could explain certain reac-
tion courses that had previously
been difficult to understand. This
gave rise to unusually intensive
research activity—both theoreti-
cal and practical—in many parts
of the world.
Fukui developed the theory that
during chemical reactions molecules
share loosely bonded electrons,
which occupy so-called frontier
orbitals. This theory advanced the under-
standing of the mechanism of chemical
reactions, especially in the production of
organic compounds. Fukui showed that
certain properties of the orbits of the most
loosely bound electrons and of the “most
easily accessible” unoccupied electronic
orbitals (which he called “frontier orbitals”)
had unexpected significance for the chem-
ical reactivity of molecules.
Building on his frontier orbital research,
Fukui expanded his research into formu-
lating the path of chemical reactions, and
he published his first paper on the topic
in 1970. In his autobiography listed on the
Nobel website (www.nobel.se/chemistry/
laureates/1981/fukui-autobio.html), he
commented on the findings in this paper:
“This simple idea served to provide infor-
mation on the geometrical shape of react-
ing molecules, and I was able to make the
C h e m i s t r y C h r o n i c l e s
J
ULIE
L. M
C
D
OWELL
AND
J
ULIA
B
ELCHER
Fukui’s Frontiers
The first Japanese scientist to win a Nobel Prize
introduced the concept of frontier orbitals.
Kenichi Fukui at a 1981 Nobel Prize committee reception.
role of the frontier orbitals in chemical
reactions more distinct through visualiza-
tion, by drawing their diagrams.”
Fukui shared the 1981 Nobel Prize in
Chemistry with Roald Hoffmann for their
theories on the course of chemical reac-
tions. Known for his calm demeanor, Fukui
was said to be gracious but composed when
informed that he won this prestigious prize.
“I am just another chemist scholar,” he said,
and feared that the publicity would disrupt
his commitment to a peaceful existence.
Although his earliest paper outlining
the theories of frontier orbitals was ignored,
Fukui’s (and Hoffmann’s) method of attack-
ing difficult and complicated problems
succeeded because they made generaliza-
tions through simplifications. Today, their
method of conceiving the course of chem-
ical reactions is used by, among others,
chemists studying life processes and
chemists making new drugs. Pharmaceuti-
cal and fine chemical companies use Fukui’s
ideas and methods to predict optimum
conditions for a particular reaction path-
way and to minimize unwanted side reac-
tions. This level of analysis enables phar-
maceutical and chemical manufacturers to
yield highly specific and pure products.
Honors Accrue
By the end of the 1960s, Fukui had earned
an international reputation as a respect-
ed scientist. In 1970, he taught at the
Illinois Institute of Technology as a Nation-
al Science Foundation senior foreign scien-
tist. In 1981, the year he won the Nobel
Prize, he was named a foreign fellow of the
National Academy of Science. The follow-
ing year, Fukui was named both professor
emeritus of Kyoto University and president
of the Kyoto Institute of Technology. He
served as president of the Chemical Soci-
ety of Japan from March 1983 to Febru-
ary 1984. In addition, Fukui was known
for his efforts to promote science educa-
tion in Japan during the later years of his
life and was the director of the Institute
for Fundamental Chemistry (Kyoto) from
1988 to 1998.
Fukui died of cancer at the age of 79
in January 1998. His obituary in The
Independent, a London newspaper, remem-
bers Fukui as a “modest, retiring man who
hated any kind of publicity. He led a
quiet life with his family and a few friends,
with whom he loved to drink sake and to
play music, for he was an excellent singer
of French and German songs.”
“I must confess that, when I was writ-
ing the 1952 paper, I never imagined I
would be coming to Stockholm to receive
the Nobel Prize 30 years later,” he wrote
in his autobiography. “The possibility
became a reality through the good circum-
stances in which I found myself: with my
teachers, my colleagues and students,
and of course, my parents and family.”
Further Reading
Fukui, K., Fujimoto, H., Eds. Frontier Orbitals and
Reaction Paths: Selected Papers of Kenichi Fukui;
World Scientific Publishing Co.: Singapore, 1997.
Autobiographical sketch for the Nobel e-Museum;
www.nobel.se/chemistry/laureates/1981/
fukui-autobio.html.
Julie L. McDowell is an assistant editor
and Julia Belcher is an associate editor
of Today’s Chemist at Work. Send your
comments or questions about this article to
tcaw@acs.org or to the Editorial Office
address on page 6. ◆
52 T
ODAY
’
S
C
HEMIST AT
W
ORK
O
CTOBER
2002
www.tcawonline.org
Advertisers
Shimadzu Scientific
Instruments
www.shimadzu.com
Reader Service No. 35
Varian Australia
www.varian.com
Reader Service No. 59
Silverson Machines
www.silverson.com
Reader Service No. 36