What is Allylic Carbon?
Allylic Carbon and Vinylic Carbon atoms are two types of double-bonded carbon. The standard formula for the vinyl group is R-CH=CH2, where R is linked to the vinylic position and both carbon atoms are double-bonded.
In the Modern Periodic Table, the atomic numbers of all known elements increase from left to right. There are 18 vertical columns referred to as groups, and 7 horizontal rows referred to as periods.
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The bottom section of the periodic table is comprised of two series of 14 elements known as f-block elements. The left side of the modern Periodic Table is dominated by metals, whereas the right side contains non-metals. Some elements have properties between those of metals and nonmetals. These elements are referred to as metalloids and are situated as a zigzag line between metals and non-metals.
Allylic Carbon Meaning
Carbon atoms with double bonds can be classed as either vinylic or allylic. The standard formula for the vinyl group is R-CH=CH2, where R is linked to the vinylic position and both carbon atoms are double-bonded.
- Both carbon atoms are sp2 hybridized because they form a double covalent bond. Additionally, the allylic position resembles the vinylic position. The allylic carbon is covalently bound to a carbon atom that is doubly covalently bonded to a second carbon atom.
- The general formula for allyl is R-CH2-CH=CH2, with the carbon atom denoted by an asterisk representing an allylic carbon atom. In contrast to the vinyl group, the allylic carbon atom is sp3 hybridized due to its solitary covalent link with CH=CH2.
- It lends special chemical properties to the allylic group, and the presence of this group in various compounds results in the formation of allylic compounds, which are employed in the production of various natural goods such as natural rubber, terpenes, etc.
Allylic Carbon Atoms
The allylic carbon atom is the sp3 hybridized carbon atom bound to the -CH=CH2 group in the allylic group RCH2-CH=CH2.
The highlighted carbon atom in propene, for example, is the allylic carbon atom (CH3-CH=CH2) Similarly, the carbon atoms adjacent to the double bond in cyclohexene are allylic carbon atoms.
Hydrocarbons
Organic compounds are made up of various components that share a parent carbon chain. Hydrocarbons are the most frequently occurring organic substances. They are mostly made of carbon and hydrogen.
- Carbon possesses tetravalency, which allows it to make four covalent bonds with the same or distinct elements.
- Carbon exhibits catenation and can generate diverse chemical compounds due to its tetravalency.
- Catenation is the capability of carbon and other elements to create covalent bonds with themselves.
- Based on the number of carbon atoms bound to a carbon atom, it can be classified as primary, secondary, or tertiary.
- A primary carbon atom is a carbon atom that is covalently connected to another carbon atom.
For instance, in the ethane molecule (CH3-CH3), both carbon atoms are bound to another carbon atom, hence both carbon atoms serve as the principal carbon atom. The secondary carbon atom is covalently bound to the other two carbon atoms, while the tertiary carbon atom is covalently bonded to three carbon atoms.
Allylic Carbocation
Carbocations are ionic species with a positive charge on the molecule’s carbon atom. Typically, they occur as intermediates during chemical processes. Steric hindrance and the +I impact of alkyl groups linked to the C+ of the carbocation determine its stability.
As the +I effect grows as a result of the positively charged carbon atom of the carbocation, the positive charge on the carbocation decreases. Therefore, as the number of alkyl groups on C+ grows, so does the stability of the carbocation.
Therefore, the carbocation stability order can be expressed as
Tertiary Carbocation > Secondary Carbocation > Primary Carbocation
- If the carbon atom in the allylic group is positively charged, it forms an allylic carbocation. The stability of the allylic carbocation results from the delocalization of electrons on carbon atoms.
- Similarly, the formal charge on the allylic carbon of the carbocation of cyclohexene is 1 and it is stabilized by resonance with the pi-bond.
- If the allylic carbon atom is connected to a single carbon atom and carries a +1 charge, this is referred to as a primary allylic carbocation. As the primary carbon atom has a formal charge of +1, this is a primary allylic carbocation.
- As with cyclohexene cation, the +1 formal charge is distributed on the secondary carbon atom of the secondary allylic carbocation.
- On a tertiary carbon atom of the cation, a tertiary allylic carbocation bears a +1 charge.
Frequently Asked Questions – FAQs
Q.1 Are allyl and vinyl the same?
Both allyl and vinyl groups share structural similarities with minor differences. The quantity of carbon and hydrogen atoms is the main distinction between these two structural elements.
Q.2 Why is vinyl less stable than allylic?
Allyl carbocation is more stable than Vinyl carbocation because it is resonance stabilized, whereas the positive charge on sp hybridized carbon is more unstable in vinyl carbocation.
Q.3 What is an allyl anion?
Generally, allylation is the addition of an allyl anion corresponding to an organic electrophile. Carbonyl allylation is a type of chemical reaction in which an active allyl group is added to the carbonyl group, resulting in the formation of allylic tertiary alcohol.
Q.4 How can you identify benzylic carbon?
A benzylic carbon is merely the saturated carbon, whereas a benzyl group is a benzene ring with another ring connected one carbon away. Left is benzyl bromide (or bromophenyl methane), whereas right is phenyl bromide (or bromobenzene).
Q.5 What is allyl alcohol used for?
Allyl alcohol is a raw ingredient for the manufacturing of glycerol, as well as a precursor to a variety of specialty chemicals, including flame-resistant polymers, drying oils, and plasticizers. Allyl alcohol is the least abundant of the allylic alcohols.
