Preferred Label : chair, boat, twist;
IUPAC definition : If carbon atoms 1, 2, 4 and 5 of cyclohexane occupy coplanar positions and when carbon
atoms 3 and 6 are on opposite sides of the plane the conformation (of symmetry group
i D /i sub 3d /sub ) is called a chair form. The same term is applied to similar
conformations of analogous saturated six-membered ring structures containing hetero-atoms
and/or bearing substituent groups, but these conformations may be distorted from the
exact i D /i sub 3d /sub symmetry. For cyclohexane and most such analogues, the
chair form is the most stable conformation. If the cyclohexane conformation has no
centre of symmetry but possesses two planes of symmetry, one of them bisecting the
bonds between atoms 1 and 2 and between 4 and 5 and the other plane passing through
atoms 3 and 6 (which lie out of the plane and on the same side of the plane containing
1, 2, 4 and 5), that conformation (of symmetry group i C /i sub 2v /sub ) is called
a boat form and it is generally not a stable form. Again, this term is also applied
to structural analogues. The conformation of i D /i sub 2 /sub symmetry passed
through in the interconversion of two boat forms of cyclohexane is called the twist
form (also known as skew boat, skew form and stretched form). In a five-membered
ring a conformation in which two adjacent atoms are maximally displaced, in opposite
directions, relative to the plane containing the other three carbon atoms has been
called a half-chair but is better called a twist conformation.;
Origin ID : C00964;
See also
If carbon atoms 1, 2, 4 and 5 of cyclohexane occupy coplanar positions and when carbon
atoms 3 and 6 are on opposite sides of the plane the conformation (of symmetry group
i D /i sub 3d /sub ) is called a chair form. The same term is applied to similar
conformations of analogous saturated six-membered ring structures containing hetero-atoms
and/or bearing substituent groups, but these conformations may be distorted from the
exact i D /i sub 3d /sub symmetry. For cyclohexane and most such analogues, the
chair form is the most stable conformation. If the cyclohexane conformation has no
centre of symmetry but possesses two planes of symmetry, one of them bisecting the
bonds between atoms 1 and 2 and between 4 and 5 and the other plane passing through
atoms 3 and 6 (which lie out of the plane and on the same side of the plane containing
1, 2, 4 and 5), that conformation (of symmetry group i C /i sub 2v /sub ) is called
a boat form and it is generally not a stable form. Again, this term is also applied
to structural analogues. The conformation of i D /i sub 2 /sub symmetry passed
through in the interconversion of two boat forms of cyclohexane is called the twist
form (also known as skew boat, skew form and stretched form). In a five-membered
ring a conformation in which two adjacent atoms are maximally displaced, in opposite
directions, relative to the plane containing the other three carbon atoms has been
called a half-chair but is better called a twist conformation.