War II, although none were used in
combat.
nitrogenous base A basic compound containing nitrogen. The term
is used especially of organic ring
compounds, such as adenine, guanine, cytosine, and thymine, which
are constituents of nucleic acids. See
amine salts.
nitroglycerine An explosive made
by reacting 1,2,3-trihydroxypropane
(glycerol) with a mixture of concentrated sulphuric and nitric acids.
Despite its name and method of
preparation, it is not a nitro compound, but an ester of nitric acid,
CH 2 (NO 3 )CH(NO 3 )CH 2 (NO 3 ). It is used
in dynamites.
nitro group See nitro compounds.
nitronium ion See nitryl ion.
nitroparafÜn See nitroalkane.
nitrosamines A group of carcinogenic compounds with the general
formula RR′NNO, where R and R′ are
side groups with a variety of possible
structures. Nitrosamines, which are a
component of cigarette smoke, cause
cancer in a number of organs, particularly in the liver, kidneys, and
lungs. An example of a nitrosamine
is dimethylnitrosamine, which has
two methyl side groups (CH 3 –).
nitrosonium ion The positive ion
NO
+ , present in certain salts such as
the chlorate (NO
+ ClO 4 ) and the
boroÛuoride (NO
+ BF 4 ).
nitrosyl ion The ion NO
+ . See nitrogen monoxide.
nitrous acid A weak acid, HNO 2 ,
known only in solution and in the
gas phase. It is prepared by the action of acids upon nitrites, preferably
using a combination that removes
the salt as an insoluble precipitate
(e.g. Ba(NO 2 ) 2 and H 2 SO 4 ). The solutions are unstable and decompose on
heating to give nitric acid and nitrogen monoxide. Nitrous acid can function both as an oxidizing agent
(forms NO) with I
– and Fe
2+ , or as a
reducing agent (forms NO 3
– ) with, for
example, Cu
2+ ; the latter is most
common. It is widely used (prepared
in situ) for the preparation of diazonium compounds in organic chemistry. The full systematic name is
dioxonitric(III) acid.
nitrous oxide See dinitrogen
oxide.
nitryl ion (nitronium ion) The ion
NO 2
+ , found in mixtures of nitric acid
and sulphuric acid and solutions of
nitrogen oxides in nitric acid. Nitryl
salts, such as NO 2
+ ClO 4
–
, can be isolated but are extremely reactive. Nitryl ions generated in situ are used for
*nitration in organic chemistry.
NMR See nuclear magnetic resonance.
nobelium Symbol No. A radioactive
metallic transuranic element belonging to the *actinoids; a.n. 102; mass
number of most stable element 254
(half-life 55 seconds). Seven isotopes
are known. The element was Ürst
identiÜed with certainty by Albert
Ghiorso and Glenn Seaborg (1912–99)
in 1966.
A
• Information from the WebElements site
noble gases (inert gases; rare
gases; group 18 elements) A group
of monatomic gaseous elements
forming group 18 (formerly group 0)
of the *periodic table: helium (He),
neon (Ne), argon (Ar), krypton (Kr),
xenon (Xe), and radon (Rn). The electron conÜguration of helium is 1s
2 .
The conÜgurations of the others terminate in ns
2
np
6 and all inner shells
are fully occupied. The elements thus
represent the termination of a period
and have closed-shell conÜguration
nitrogenous base
376
n
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combat.
nitrogenous base A basic compound containing nitrogen. The term
is used especially of organic ring
compounds, such as adenine, guanine, cytosine, and thymine, which
are constituents of nucleic acids. See
amine salts.
nitroglycerine An explosive made
by reacting 1,2,3-trihydroxypropane
(glycerol) with a mixture of concentrated sulphuric and nitric acids.
Despite its name and method of
preparation, it is not a nitro compound, but an ester of nitric acid,
CH 2 (NO 3 )CH(NO 3 )CH 2 (NO 3 ). It is used
in dynamites.
nitro group See nitro compounds.
nitronium ion See nitryl ion.
nitroparafÜn See nitroalkane.
nitrosamines A group of carcinogenic compounds with the general
formula RR′NNO, where R and R′ are
side groups with a variety of possible
structures. Nitrosamines, which are a
component of cigarette smoke, cause
cancer in a number of organs, particularly in the liver, kidneys, and
lungs. An example of a nitrosamine
is dimethylnitrosamine, which has
two methyl side groups (CH 3 –).
nitrosonium ion The positive ion
NO
+ , present in certain salts such as
the chlorate (NO
+ ClO 4 ) and the
boroÛuoride (NO
+ BF 4 ).
nitrosyl ion The ion NO
+ . See nitrogen monoxide.
nitrous acid A weak acid, HNO 2 ,
known only in solution and in the
gas phase. It is prepared by the action of acids upon nitrites, preferably
using a combination that removes
the salt as an insoluble precipitate
(e.g. Ba(NO 2 ) 2 and H 2 SO 4 ). The solutions are unstable and decompose on
heating to give nitric acid and nitrogen monoxide. Nitrous acid can function both as an oxidizing agent
(forms NO) with I
– and Fe
2+ , or as a
reducing agent (forms NO 3
– ) with, for
example, Cu
2+ ; the latter is most
common. It is widely used (prepared
in situ) for the preparation of diazonium compounds in organic chemistry. The full systematic name is
dioxonitric(III) acid.
nitrous oxide See dinitrogen
oxide.
nitryl ion (nitronium ion) The ion
NO 2
+ , found in mixtures of nitric acid
and sulphuric acid and solutions of
nitrogen oxides in nitric acid. Nitryl
salts, such as NO 2
+ ClO 4
–
, can be isolated but are extremely reactive. Nitryl ions generated in situ are used for
*nitration in organic chemistry.
NMR See nuclear magnetic resonance.
nobelium Symbol No. A radioactive
metallic transuranic element belonging to the *actinoids; a.n. 102; mass
number of most stable element 254
(half-life 55 seconds). Seven isotopes
are known. The element was Ürst
identiÜed with certainty by Albert
Ghiorso and Glenn Seaborg (1912–99)
in 1966.
A
• Information from the WebElements site
noble gases (inert gases; rare
gases; group 18 elements) A group
of monatomic gaseous elements
forming group 18 (formerly group 0)
of the *periodic table: helium (He),
neon (Ne), argon (Ar), krypton (Kr),
xenon (Xe), and radon (Rn). The electron conÜguration of helium is 1s
2 .
The conÜgurations of the others terminate in ns
2
np
6 and all inner shells
are fully occupied. The elements thus
represent the termination of a period
and have closed-shell conÜguration
nitrogenous base
376
n
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