What are the conditions for ring expansion?

Ring expansions occur as a carbocation rearrangement when an unstable cycloalkane is near a carbocation. You will come across ring expansion mechanisms during alkene reactions and later in SN1 and E1 reactions.

What causes a hydride shift?

1,2-HYDRIDE SHIFTS Whenever you have a more substituted carbon adjacent to a cationic carbon, a 1,2-hydride shift would shift the positive charge over to a carbon that can better stabilize itself.

How does a methyl shift occur?

The key difference between hydride and methyl shift is that a hydride shift can occur when a hydrogen atom moves to a carbon atom bearing a positive charge from an adjacent carbon in the same molecule whereas methyl shift occurs when a methyl group moves to a carbon atom bearing a positive charge from an adjacent …

What type of compounds undergo ring expansion in demjanov rearrangement?

4 Cyclic alkenes and cyclic ketones: ring expansion and ring contraction. The oxidative rearrangement of cyclic alkenes and ketones often leads to ring expansion63 or ring contraction reactions.

What is a hydride shift?

Hydride shift is a rearrangement of a hydrogen atom in a carbocation to make the intermediate structure more stable. It is generally observed in rearrangement reactions. After shifting a hydrogen atom from one carbon to another, structural isomers of compounds are formed.

How do you rearrange carbocations?

There are two types of carbocation rearrangements: a hydride shift and an alkyl shift. Once rearranged, the resultant carbocation will react further to form a final product which has a different alkyl skeleton than the starting material.

What is an alkyl shift?

A 1,2-alkyl shift is a carbocation rearrangement in which an alkyl group migrates to the carbon atom bearing the formal charge of +1 (carbon 2) from an adjacent carbon atom (carbon 1), e.g. see also 1,2-hydride shift, 1,2-aryl shift.

What carbocations are most likely to rearrangements?

Carbocation rearrangements occur most frequently on secondary carbocations. Simple alkyl primary carbocations are too high in energy to form so you don’t tend to see a primary carbocation.

What causes a methyl shift?

Why is the ring strain of cyclohexane reduced in conformers?

The ring strain is reduced in conformers due to the rotations around the sigma bonds, which decreases the angle and torsional strain in the ring. The non-planar structures of cyclohexane are very stable compared to cyclopropane and cyclobutane, and will be discussed in more detail in the next section.

Which is more stable pentane or 2 3 dimethylpentane?

Pentane has a heat of combustion of -782 kcal/mol, while that of its isomer, 2,2-dimethylpropane (neopentane), is –777 kcal/mol. These values indicate that 2,3-dimethylpentane is 5 kcal/mol more stable than pentane, since it has a lower heat of combustion.

Why is cyclohexane less stable than cyclopropane?

In 1890, the famous German organic chemist, A. Baeyer, suggested that cyclopropane and cyclobutane are less stable than cyclohexane, because the the smaller rings are more “strained”. There are many different types of strain that contribute to the overall ring strain in cycloalkanes, including angle strain, torsional strain, and steric strain.

Can the absorption of pentane via the lungs be predicted?

From results of studies which measured respiratory absorption of n-hexane and n-heptane significant absorption of pentane via the lungs /can be predicted/. Dermal absorption of liquid n-pentane would not be expected to be significant, since it would rapidly evaporate from the skin