Strain of Cycloalkanes

Nonplanar

Nonplanar

________ or puckered conformations are favored in all cycloalkanes bigger than cyclopropane.

Cyclohexane

________ adopts a number of puckered conformations that interconvert via C- C bonds.

dynamic equilibrium

Exists as a(n) ________ of five envelope conformations in which each carbon atoms alternates as the out of plane carbon.

envelope conformation

In the ________, the average C- C- C bond angle is reduced to 105.

Cyclic alkanes

________ of 4 carbons or more have rapidly interconverting conformations with varying degrees of torsional strain along their C- C single bonds.

cyclopropane

Since ________ is planar, there are 6 pairs of C- H bonds that are fully eclipsed and introduce torsional strain.

Diaxial interaction

________: the steric strain arising from interaction between an axial substituent and an axial hydrogen (or another group) on the same side of a chair conformation of a cyclohexane ring.

energies of cyclic alkanes

The structures and ________ are highly dependent on the size of their rings.

C C C bond angles

All ________ are 110.9 (minimizing angle strain) and all hydrogens on adjacent carbons are staggered with respect to one another (minimizing torsional strain)

Boat conformation

________: a nonplanar conformation of a cyclohexane ring in which carbons 1 and 4 of the ring are bent toward each other.

nonoptimal bond angles

Small ring strain: a strain associated with ring sizes below six that arises from ________ (optimal angle is 109.5)

Envelope conformation

________: 4 carbons are in the same plane and the fifth one is bent upward (like a flap on an envelope)

Small ring strain

a strain associated with ring sizes below six that arises from nonoptimal bond angles (optimal angle is 109.5)

Observed bond angles of cyclopropane

60 (much less than 109.5)

Envelope conformation

4 carbons are in the same plane and the fifth one is bent upward (like a flap on an envelope)

6 bonds are axial bonds

a bond to a chair conformation of cyclohexane that extends from the ring parallel to the imaginary axis through the center of the ring; a bond that lies roughly perpendicular to the equator of the ring

6 bonds are 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 the ring

Boat conformation

a nonplanar conformation of a cyclohexane ring in which carbons 1 and 4 of the ring are bent toward each other

Twist-boat conformation

a nonplanar conformation of a cyclohexane ring that is twisted from and is slightly more stable than a boat conformation

Diaxial interaction

the steric strain arising from interaction between an axial substituent and an axial hydrogen (or another group) on the same side of a chair conformation of a cyclohexane ring

Since cyclopropane is planar,

there are 6 pairs of C-H bonds that are fully eclipsed and introduce torsional strain

If cyclopentane were planar,

all C-C-C bond angles would be 108