5-Dehydro-m-xylylene
Encyclopedia
5-Dehydro-m-xylylene is an aromatic
organic
triradical and the first known organic molecule to violate Hund's Rule
.
Its electronic ground state is an "open-shell
doublet" rather than a quartet; that is, it contains three low-spin
coupled unpaired electrons in three singly occupied molecular orbital
s. Because there are radical electrons in both spin states, this compound is said to exhibit antiferromagnetism
. Though similar ground states are observed in molecules containing transition metal atoms, it is unprecedented in organic molecules.
The 5-dehydro-m-xylylene anion (DMX-) has also been studied extensively. It has a triplet ground state consisting of a phenyl anion and a m-xylylene biradical.
Aromaticity
In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...
organic
Organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...
triradical and the first known organic molecule to violate Hund's Rule
Hund's rule of Maximum Multiplicity
Hund's Rule of Maximum Multiplicity is an observational rule which states that a greater total spin state usually makes the resulting atom more stable. Accordingly, it can be taken that if two or more orbitals of equal energy are available, electrons will occupy them singly before filling them in...
.
Its electronic ground state is an "open-shell
Open shell
In the context of atomic orbitals, an open shell is a valence shell which is not completely filled with electrons or that has not given all of its valence electrons through chemical bonds with other atoms or molecules during a chemical reaction. Atoms generally reach a noble gas configuration in a...
doublet" rather than a quartet; that is, it contains three low-spin
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...
coupled unpaired electrons in three singly occupied molecular orbital
Molecular orbital
In chemistry, a molecular orbital is a mathematical function describing the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region. The term "orbital" was first...
s. Because there are radical electrons in both spin states, this compound is said to exhibit antiferromagnetism
Antiferromagnetism
In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usuallyrelated to the spins of electrons, align in a regular pattern with neighboring spins pointing in opposite directions. This is, like ferromagnetism and ferrimagnetism, a manifestation of ordered magnetism...
. Though similar ground states are observed in molecules containing transition metal atoms, it is unprecedented in organic molecules.
The 5-dehydro-m-xylylene anion (DMX-) has also been studied extensively. It has a triplet ground state consisting of a phenyl anion and a m-xylylene biradical.