Ring flip of cyclohexane

How does the rotation around carbon-carbon o bonds and the ring flip of cyclohexane rings affect an NMR spectrum Because these processes are rapid at room temperamre, an NMR spectrum records an average of all conformations that interconvert. 

Amide C—N Bond Rotation and Ring-Flip of Cyclohexanes... 

Bond rotation of amides and ring-flip of cyclohexanes... 

Flexibility. Many rings are highly mobile. One example of this phenomenon is the ring flip of cyclohexane. You must be able to flip cyclohexanes and draw the two interconverting chair forms well. 

A substituent is less crowded and more stable when it is equatorial than when It IS axial on a cyclohexane ring Ring flipping of a monosubsti tuted cyclohexane allows the substituent to become equatorial... 

The answer is related to the very rapid rate of ring flipping m cyclohexane... 

The best way to understand ring flipping in cyclohexane is to view the animation of Figure 3.15 in Learning By Modeling. 

Ring flipping Synonymous with ring inversion of cyclohexane and related compounds. 

The words NMR spectrum and a change in the spectrum with temperature always mean that some groups in the molecule are interchanging positions through some sort of molecular motion, typically bond rotation (as here) or ring flipping in cyclohexanes. 

Figure 4-11 Chair-chair interconversion C ring flipping ) in cyclohexane. In the process, which is rapid at room temperature, a (green) carison at one end of the molecule moves up while its counterpart (also green) at the other end moves down. All groups originally in axial positions (red in the structure at the left) become equatorial, and those that start in equatorial positions (blue) become axial.

Conformational inversion (ring flipping) is rapid in cyclohexane and causes all axial bonds to become equatorial and vice versa As a result a monosubstituted derivative of cyclohexane adopts the chair conforma tion in which the substituent is equatorial (see next section) No bonds are made or broken in this process... 

Among all the isomers as 1 2 dichlorocycio hexane is unique in that the ring flipping process typ ical of cyclohexane derivatives (Section 3 9) converts it to its enantiomer... 

The rate of ring flipping can be slowed down by lowering the temperature At tern peratures on the order of — 100°C separate signals are seen for the axial and equatorial protons of cyclohexane... 

Ring inversion (Section 3 9) Process by which a chair conforma tion of cyclohexane is converted to a mirror image chair All of the equatonal substituents become axial and vice versa Also called ring flipping or chair-chair interconversion... 

Because chair cyclohexane has two kinds of positions, axial and equatorial, we might expect to find two isomeric forms of a monosubstituted cyclohexane. In fact, we don t. There is only one methylcyclohexane, one bromocydohexane, one cycJohexanol (hydroxycyclohexane), and so on, because cyclohexane rings are confbnnationally mobile at room temperature. Different chair conformations readily interconvert, exchanging axial and equatorial positions. This interconversion, usually called a ring-flip, is shown in Figure 4.11. 

Thomson fOV Click Organic Interactive to learn to recognize the most stable conformations of cyclohexanes following ring-flips. 

Chair cyclohexanes are conformationally mobile and can undergo a ring-flip, which interconverts axial and equatorial positions. Substituents on the ring are more stable in the equatorial position because axial substituents cause 1,3-diaxial interactions. The amount of 1,3-diaxial steric strain caused by an axial substituent depends on its hulk. 

How many electronically nonequivalent kinds of protons and how many kinds of carbons are present in the following compound Don t forget that cyclohexane rings can ring-flip. 

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