an insoluble precipitate, then B may
be carried down with the precipitate
of A, even though it is soluble under
the conditions. This can occur by occlusion or absorption.
cordite An explosive mixture of cellulose nitrate and nitroglycerin, with
added plasticizers and stabilizers,
used as a propellant for guns.
core orbital An atomic orbital that
is part of the inner closed shell of an
atom. Unlike the valence orbitals,
which are the atomic orbitals of the
valence shell of an atom, core orbitals on one atom have a small overlap with core orbitals on another
atom. They are therefore usually ignored in simple calculations of chemical bonding.
Corey–Pauling rules A set of
rules, formulated by Robert Corey
and Linus *Pauling, that govern the
secondary nature of proteins. The
Corey–Pauling rules are concerned
with the stability of structures provided by *hydrogen bonds associated
with the –CO–NH– peptide link. The
Corey–Pauling rules state that:
(1) All the atoms in the peptide link
lie in the same plane.
(2) The N, H, and O atoms in a hydrogen bond are approximately on a
straight line.
(3) All the CO and NH groups are involved in bonding.
Two important structures in which
the Corey–Pauling rules are obeyed
are the alpha helix and the *beta
sheet.
CORN rule See absolute configuration.
correlation diagram A diagram
that relates the energy levels of separate atoms to the energy levels of diatomic molecules and united atoms,
the two limiting states being correlated with each other. Using this diagram, the types of molecular orbital
possible for the molecules and their
order as a function of increasing energy can be seen as a function of interatomic distance. Lines are drawn
linking each united-atom orbital to a
separated atom orbital. An important
rule for determining which energy
levels correlate is the noncrossing
rule. This states that two curves of
energy plotted against interatomic
distance never cross if the invariant
properties (e.g. parity, spin, etc.) are
the same.
correlation functions Quantities
used in condensed-matter physics
that are *ensemble averages of products of such quantities as *density at
different points in space. Each particle affects the behaviour of its neighbouring particles, so creating
correlations, the range of which is at
least as long as the range of the intermolecular forces. Thus, correlation
functions contain a great deal of information about systems in condensed-matter physics. Correlation
functions can be measured in considerable detail, frequently by experiments involving scattering of such
particles as neutrons or of *electromagnetic radiation (e.g. light or Xrays) and can be calculated
theoretically using *statistical mechanics.
correlation spectroscopy (COSY)
A type of spectroscopy used in *nuclear magnetic resonance (NMR) in
which the pulse sequence used is:
90°x – t 1 – 90°x – acquire (t 2 ). The
delay t 1 is variable and a series of acquisitions is made. Fourier transforms are then performed on both
the delay t 1 and the real time t 2 . The
information thus gained can be
shown on a diagram that plots contours of signal intensity. This representation of the information enables
NMR spectra to be interpreted more
145
correlation spectroscopy
c
www.AzShimi.ir www.AzShimi.com
be carried down with the precipitate
of A, even though it is soluble under
the conditions. This can occur by occlusion or absorption.
cordite An explosive mixture of cellulose nitrate and nitroglycerin, with
added plasticizers and stabilizers,
used as a propellant for guns.
core orbital An atomic orbital that
is part of the inner closed shell of an
atom. Unlike the valence orbitals,
which are the atomic orbitals of the
valence shell of an atom, core orbitals on one atom have a small overlap with core orbitals on another
atom. They are therefore usually ignored in simple calculations of chemical bonding.
Corey–Pauling rules A set of
rules, formulated by Robert Corey
and Linus *Pauling, that govern the
secondary nature of proteins. The
Corey–Pauling rules are concerned
with the stability of structures provided by *hydrogen bonds associated
with the –CO–NH– peptide link. The
Corey–Pauling rules state that:
(1) All the atoms in the peptide link
lie in the same plane.
(2) The N, H, and O atoms in a hydrogen bond are approximately on a
straight line.
(3) All the CO and NH groups are involved in bonding.
Two important structures in which
the Corey–Pauling rules are obeyed
are the alpha helix and the *beta
sheet.
CORN rule See absolute configuration.
correlation diagram A diagram
that relates the energy levels of separate atoms to the energy levels of diatomic molecules and united atoms,
the two limiting states being correlated with each other. Using this diagram, the types of molecular orbital
possible for the molecules and their
order as a function of increasing energy can be seen as a function of interatomic distance. Lines are drawn
linking each united-atom orbital to a
separated atom orbital. An important
rule for determining which energy
levels correlate is the noncrossing
rule. This states that two curves of
energy plotted against interatomic
distance never cross if the invariant
properties (e.g. parity, spin, etc.) are
the same.
correlation functions Quantities
used in condensed-matter physics
that are *ensemble averages of products of such quantities as *density at
different points in space. Each particle affects the behaviour of its neighbouring particles, so creating
correlations, the range of which is at
least as long as the range of the intermolecular forces. Thus, correlation
functions contain a great deal of information about systems in condensed-matter physics. Correlation
functions can be measured in considerable detail, frequently by experiments involving scattering of such
particles as neutrons or of *electromagnetic radiation (e.g. light or Xrays) and can be calculated
theoretically using *statistical mechanics.
correlation spectroscopy (COSY)
A type of spectroscopy used in *nuclear magnetic resonance (NMR) in
which the pulse sequence used is:
90°x – t 1 – 90°x – acquire (t 2 ). The
delay t 1 is variable and a series of acquisitions is made. Fourier transforms are then performed on both
the delay t 1 and the real time t 2 . The
information thus gained can be
shown on a diagram that plots contours of signal intensity. This representation of the information enables
NMR spectra to be interpreted more
145
correlation spectroscopy
c
www.AzShimi.ir www.AzShimi.com