Main Difference – Allyl vs Vinyl
Allyl and vinyl are two different organic functional groups. Both have C-C double bonds but in different positions. In vinyl group, C=C is directly attached to the rest of the chain. In contrast to vinyl, allyl group is attached to the rest of the molecule through –CH2 group. This is the main difference between Allyl and Vinyl groups.
What is Vinyl
Vinyl indicates the –CH=CH2 functional group, which can be formed by removing hydrogen from ethylene molecule. Therefore, the general molecular formula of vinyl compounds is R- CH=CH2, where R is any other group of atoms. Vinylic groups have sp2 hybridized carbon atoms. These compounds are very reactive, and readily polymerize to form vinyl polymers. Polyvinyl chloride, polyvinyl fluoride, and polyvinyl acetate are some examples of vinyl polymers. The Figure 1. Illustrates the mechanism of polyvinyl chloride synthesis.
Figure 1. Free radical vinyl polymerization mechanism
Vinylic compounds are generally used for plastic manufacturing since it is durable, cheaper, etc. In addition, vinyl has many other uses, because of its ability to be combined with various additives and modifiers.
What is Allyl
Allyl indicates a functional group with structural formula H2C=CH-CH2-R, where R is the rest of the molecule. It consists of methylene bridge (-CH2-) in between the vinyl group (-CH=CH2) and the rest of the molecule. Therefore, allyl group contains sp2 hybridized vinyl carbon atoms and sp3 hybridized allyl carbon atom. The allylic carbon atom is more reactive than normal alkanes, and it can easily form a stable carbocation because it is adjacent to vinyl carbon that can delocalize electrons to stabilize the positive charge. The Figure 2. Illustrates the resonance stabilization of allylic carbocation.
Due to the stability of the carbocation, allyl compounds radially form intermediates during the reaction. For example, SN1 reaction.
Difference Between Allyl and Vinyl
General Molecular Formula
Allyl: The general molecular formula is RCH2CH=CH2. The Vinyl group is attached to rest of the molecule through –CH2– group.
Vinyl: The general molecular formula is RCH=CH2. The Vinyl group is directly attached to rest of the molecule.
Hybridization of Carbon Skeleton
Allyl: This contains sp3 hybridized allyl carbon atom, which is adjacent to sp2 hybridized carbon atom.
Vinyl: This contains sp2 hybridized carbon atoms.
Allyl: Allylic compounds are precursors to many natural products, including natural rubber and biosynthesis f terpenes.
Vinyl: Vinylic compounds can produce vinylic polymers such as PVC, PVF, PVAc, etc.
Stability of Carbocation
Allyl: Allylic carbon atom can form stable carbocations due to electron delocalization.
Vinyl: Vinylic carbocations are very unstable due to lack of p-character.