The key difference between alpha and beta carbon is that alpha carbon is the first carbon atom attached to a functional group, whereas beta carbon is the second carbon atom attached to the functional group.
The terms alpha carbon and beta carbon are very important in organic chemistry in determining factors like organic synthesis reaction products and reactivity. We can determine whether a carbon atom is an alpha or beta by identifying the location of the carbon atom relative to the functional group. However, according to IUPAC nomenclature, these carbon atoms are identified via numbers and not by Greek letters. However, this naming system also remains popular up to this date. This is because it makes it easy to identify carbon atoms adjacent to functional groups to determine their reactivity.
CONTENTS
1. Overview and Key Difference
2. What is Alpha Carbon
3. What is Beta Carbon
4. Alpha vs Beta Carbon in Tabular Form
5. Summary – Alpha vs Beta Carbon
What is Alpha Carbon?
Alpha carbon is the carbon atom located adjacent to a functional group in an organic chemical compound. Typically, carbonyl carbon atoms are alpha carbon atoms. Hydrogen atoms attached to this carbon atom are named alpha hydrogen atoms. Alpha carbon in an amino acid contains the carboxylic acid group and the amine group attached to it. We can denote alpha carbon from Cα.
Figure 01: The Chemical Structure of Nitrostyrene
however, there can be organic molecules having more than one functional group per molecule. Therefore, it can be a source of confusion. We can generally consider the functional group that is responsible for the name of the compound as the reference group in naming carbon atoms. e.g. nitrostyrene and phenethylamine are similar to each other. The former can be reduced to the latter. But the alpha carbon atom in nitrostyrene is located adjacent to the phenyl group. But in the phenethylamine molecule, this same carbon atom is located as the beta carbon because this molecule has its atoms from the opposite end of the molecule.
What is Beta Carbon?
Beta carbon is the carbon atom attached second to a functional group in an organic chemical compound. In other words, a beta-carbon atom is attached to a functional group via another carbon atom (the alpha-carbon atom). Typically, the second carbon following the carboxyl carbon is the beta-carbon atom. On the other hand, the carbon atom located farthest from the carboxyl carbon atom in a chain is named the omega carbon atom. The hydrogen atoms attached to a beta-carbon atom are named beta-hydrogen atoms. The beta carbon atom in a beta amino acid contains the carboxylic acid group and amine group attached to the adjacent carbon atom. We can denote beta carbon from Cβ.
Beta amino acids are analogous to alpha-amino acids because the amino acid group is attached to the beta carbon instead of the alpha carbon.
What is the Difference Between Alpha and Beta Carbon?
Identification of alpha and beta carbon atoms is very important in organic synthesis and identification processes. The key difference between alpha and beta carbon is that alpha carbon refers to the first carbon atom attached to a functional group, whereas beta carbon refers to the carbon atom attached second to the functional group.
The below infographic presents the differences between alpha and beta carbon in tabular form for side-by-side comparison.
Summary – Alpha vs Beta Carbon
Alpha carbon is the carbon atom located adjacent to a functional group in an organic chemical compound. Beta carbon is the carbon atom attached second to a functional group in an organic chemical compound. The key difference between alpha and beta carbon is that alpha carbon refers to the first carbon atom attached to a functional group, whereas beta carbon refers to the carbon atom attached second to the functional group.
Reference:
1. “Alpha and beta carbon.” Wikipedia. Wikipedia Foundation.
Image Courtesy:
1. “Beta-nitrostyrene” By Yikrazuul (talk) – Own work (Public Domain) via Commons Wikimedia