Chapter 2.5: Conformations of Alkane and Cycloalkanes
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What is any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond?
conformation
What type of strain is common in the eclipsed conformation?
torsional strain
Define strain
an instability within a structure associated with higher internal energy
Define gauche conformation
a conformation about a single bond of alkane in which two groups on adjacent carbons lie at a dihedral angle of 60°
What is the strain that arises when a bond angle is either compressed or expanded compared to its optimal value?
angle strain
What is the strain that arises when nonbonded atoms separated by four or more bonds are forced closer to each other than their atomic (contact) radii would allow. Steric strain is also called non-bonded interaction strain, or van der Waals strain.?
steric strain
Define chair conformation
the most stable nonplanar conformation of a cyclohexane ring; all bond angles are ~109.5°, and all bonds on adjacent carbons are staggered
What is a conformation about a carbon-carbon single bond in which atoms or groups on one carbon are as far apart as possible from atoms or groups on an adjacent carbon?
staggered conformation
What is the most stable nonplanar conformation of a cyclohexane ring; all bond angles are ~109.5°, and all bonds on adjacent carbons are staggered?
chair conformation
What is a bond to a chair conformation of cyclohexane that extends from the ring roughly perpendicular to the imaginary axis through the center of the ring, a bond that lies roughly along the equator of a cyclohexane ring?
equatorial bonds
What is a conformation about a single bond of alkane in which two groups on adjacent carbons lie at a dihedral angle of 60°?
gauche conformation
Define eclipsed conformation
a conformation about a carbon-carbon single bond in which the atoms or groups on one carbon are as close as possible to the atoms or groups on an adjacent carbon
Define torsional strain
strain that arises when nonbonded atoms separated by 3 bonds are forced from a staggered conformation to an eclipsed conformation. Also called eclipsed-interaction strain.
Define equatorial bonds
a bond to a chair conformation of cyclohexane that extends from the ring roughly perpendicular to the imaginary axis through the center of the ring, a bond that lies roughly along the equator of a cyclohexane ring
Define angle strain
the strain that arises when a bond angle is either compressed or expanded compared to its optimal value
What is a nonplanar conformation of a cyclohexane ring that is twisted from and slightly more stable than a boat conformation?
twist-boat
Define anticonformation
a conformation about a single bond of alkane in which two groups on adjacent carbons lie at the dihedral angle of 180°
Define steric strain
the strain that arises when nonbonded atoms separated by four or more bonds are forced closer to each other than their atomic (contact) radii would allow. Steric strain is also called non-bonded interaction strain, or van der Waals strain.
What is the angle created by two interesting planes?
dihedral angle (θ)
How is steric strain produced in a chair conformation?
Any group larger than an H atom will experience steric strain if it is axial
What is a conformation about a single bond of alkane in which two groups on adjacent carbons lie at the dihedral angle of 180°?
anticonformation
Define diaxial (axial-axial) interaction
refers to steric strain arising from interaction between an axial hydrogen (or other groups) on the same side of a chair conformation of a cyclohexane ring
Define dihedral angle (θ)
the angle created by two interesting planes
What is an instability within a structure associated with higher internal energy?
strain