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Allylic Carbon – Definition, Features and FAQs

Aug 12, 2022

Allylic Carbon

All existing elements are listed in ascending order in the Modern Periodic table, considering the atomic number. Allylic carbon is defined as a carbon atom connected to another carbon atom, which is bonded twice to another carbon atom. There are eighteen vertical columns and seven horizontal rows collectively called periods and groups.

The f-block element, found in two series of 14 elements, is at the bottom of the periodic table. The Modern Periodic Table’s left side is predominately made up of metals, while the right is mostly made up of non-metallic elements. A few elements positioned in the center exhibit the characteristics of both metals and nonmetals. These elements, known as metalloids, exist between metals and nonmetals in a zig-zag manner.


Elements with a high degree of reactivity and electropositivity are known as metals. In contrast to metals, nonmetals have an electronegative characteristic. One of the most often utilized nonmetals is carbon, the foundation for all other organic compounds.

Interesting Fact:

The Latin word Allium sativum, which means garlic, is the source of the name Allyl Group. Theodor Wertheim discovered an allyl derivative in garlic oil in 1844 and named it “Schwefel Allyl.” The term “allyl” refers to a wide range of H2C=CHCH2-related chemicals, some of which are useful or important in daily life, like allyl chloride. Any chemical process that imparts an allyl group to a substrate is known as allylation.


Thus, allylation is the process of joining an allyl group to a substrate, which is often another organic chemical. Allylation involves the interaction of carbanion with allyl chloride.

What is Allylic Carbon?

What is allylic? Allylic carbon can be defined as the carbon atom close to the double bond known as allylic carbon. This carbon atom is closest to the double bond atom, although it is not a component of the double bond. Or, to put it another way, this carbon atom is doubly connected to another carbon atom, which is bonded to another carbon atom. The double carbon bond atoms are sp2 hybridized. But the allylic carbon has undergone sp3 hybridization. One bond connects it to the carbon atom that has undergone sp2 hybridization. This carbon atom’s electron density is lower than the carbon atoms in the double bond.

The general formula for allylic carbon atoms can be stated as follows: CH3-CH=CH2


This carbon is unaffected by reactions that include double bonds, such as electrophilic additions, because it is not directly joined to the double bond. Allylic hydrogen is the name of hydrogen atoms connected to this allylic carbon. A bridge made of allylic carbon can join a double bond with a carbon chain. In this case, the C-H bond is weaker than typical C-H bonds. It is due to the double bond displacing the electrons surrounding this carbon. These locations are, therefore, particularly reactive.

Allylic Carbon: Features

Both carbon atoms are sp2 hybridized because they share a double covalent bond. A vinylic position is comparable to the allylic stance. It is linked to an atom of carbon that is linked twice to an additional carbon atom.


Allyl is represented by the generic formula R-CH2-CH=CH2, where the asterisk represents the allylic carbon atom. In contrast to the vinyl group, the allylic carbon atom is sp3 hybridized since it creates a single covalent bond with CH=CH2.

The presence of the allylic group in various compounds results in allylic compounds utilized to manufacture various natural goods such as natural rubber, terpenes, and many others. The allylic carbon gives the allylic group distinctive chemical properties.


Allylic and Vinylic Carbons: Key Distinction

Understanding organic compounds’ chemical or physical properties depends heavily on functional groups. If a carbon atom is directly or indirectly connected to a double bond in a structure, it is called allylic or vinylic carbon. The main distinction between allylic and vinylic carbon is that vinylic carbon is one of the two atoms that form (or share) the double bond. In contrast, allylic carbon is the carbon atom that is next to the double-bonded carbon atom.

Therefore, the distinction between allylic and vinylic carbon is related to whether the carbon atom is directly or indirectly connected to a double bond. In contrast to vinylic carbon, allylic carbon is indirectly connected to a double bond. Allylic carbon is sp3 hybridized while vinylic carbon is sp2 hybridized is another significant distinction between the two types of carbon.


Atoms of Allylic Carbon

The allylic carbon atom is the sp3 hybridized carbon atom in the group RCH2-CH=CH2 linked to the -CH=CH2 group.

For instance, in propene, the indicated carbon atom is an allylic carbon atom (CH3-CH=CH2). Similarly, the carbon atoms close to the double bond atoms are allylic in cyclohexene.



Hydrocarbons are compounds consisting of only two elements, carbon, and hydrogen. These are the most basic organic molecules and are the foundations of other organic molecules. Methane (CH4), which has only one carbon atom and four hydrogen atoms, is the most basic example of hydrocarbons. Ethane (C2H6), butane (C4H10), and propane (C3H8) are some other common examples of hydrocarbons. Natural gas and crude oil both contain hydrocarbons.

Organic compounds are the most common example of hydrocarbons. These organic compounds comprise several elements with a primary carbon chain. They are primarily composed of hydrogen and carbon atoms.

  • Tetravalency is a property of carbon that allows it to establish four covalent bonds with the same or distinct atoms.
  • Tetravalency allows carbon to exhibit catenation and create a variety of chemical compounds.
  • The ability of carbon or other elements to make covalent bonds with another element is known as catenation.
  • Depending on how many carbon atoms are connected, it can be classified as a primary, secondary, or tertiary carbon atom.
  • A primary carbon atom is bound to another carbon atom.
  • For instance, both carbon atoms in the ethane molecule (CH3-CH3) are bound to another carbon atom, making them the main carbon atom. The secondary carbon atom is linked (bound) to the other two carbon atoms, and the tertiary carbon atom is linked (bound) to three other carbon atoms.

Allylic Carbocation

The allylic carbocation can be defined as ionic species that carry positively charged carbon atoms of the molecule. They normally develop as a mediator during different chemical reactions.

The stabilization of the carbocations is influenced by the steric hindrance and +I effect of the alkyl groups connected to the C+ of the carbocation.

When the +I influences the increase of positively charged carbon atoms of the carbocation, the positive charge on the carbocation is subsequently decreased. As a result, the carbocation stability increases as the number of alkyl groups on C+ increases.

As a result, the following approach can be used to express the carbocation’s stability order.

Tertiary Carbocation > Secondary Carbocation > Primary Carbocation

  • An allylic carbocation occurs when a positive charge carries the carbon atom in the allylic group. The reduction process of electrons on carbon atoms makes the allylic carbocation stable.
  • Similar to this, the formal charge on the allylic carbon in the case of the carbocation of cyclohexene is +1, and it is stabilized by resonance with a pi-bond.
  • A main allylic carbocation is one in which the allylic carbon atom is bonded to another carbon atom with a positive charge. It is known as a main allylic carbocation because the first carbon atom in this situation has a formal charge of +1.
  • The secondary carbon atom of the secondary allylic carbocation bears a +1 formal charge, just like the cyclohexene cation.
  • The tertiary carbon atom of a cation is positively charged in a tertiary allylic carbocation.


Functional groups play a crucial role in comprehending the many physicochemical characteristics of organic compounds. Allylic carbon is the carbon atom close to the double-bonded carbon atom. Allylic Carbon is the name given to the carbon atom that is close to the double bond. Although it is not a part of the double bond, this carbon atom is the one that is closest to it. In other terms, this carbon atom is joined to a neighboring carbon atom through a double bond, and vice versa.

Frequently Asked Questions

1. What are the characteristics of allylic carbon?

Allylic carbon is composed of two carbon atoms that are doubly linked to one another.

  • An allylic group’s carbon atom undergoes sp3 hybridization.
  • An allylic carbon has a longer C-H bond length.
  • They only create one bond.
  • Allylic carbon is a link to join the double bond to the remaining molecule.

2. What is an allylic carbon?

An allylic carbon is a carbon atom that is joined to two other carbon atoms. Many physiological or biochemical compounds, such as cholesterol and some vitamins, contain allylic carbon atoms.

3. Describe the arrangement of the atoms in allylic carbon.

A carbon atom connected to two other carbon atoms, where one of the atoms is also joined to a hydrogen atom, is said to be allylic. Alkenes and alkynes are two different classes of hydrocarbons; both include this kind of carbon atom. Alkynes can be defined as bonds having one or more double bonds, while alkenes have one or more triple bonds.

4. What is allylic carbocation?

Allylic carbocation is a carbocation form with three other carbon atoms bound to the carbon atom. The allylic carbon atom is the carbon atom that makes up an allylic carbocation. Due to their extreme instability, allylic carbocations frequently occur when organic molecules are subjected to radioactivity or high temperatures. Including electron-donating groups, like alkyl groups on the carbon atom, helps stabilize allylic carbocations.

Allylic Carbon


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