Question

Which of the following alkane on monochlorination gives racemic mixture? (1) neopentane (2) \(\mathrm{n}\) -butane (3) 2,3 -dimethyl butane (4) \(2,2,3,3\) -tetramethyl butane

Short answer

2,3-Dimethylbutane

Step-by-step solution

- Understanding Monochlorination

Monochlorination refers to replacing one hydrogen atom in an alkane with a chlorine atom, forming a chlorinated derivative.

- Identifying the Chiral Carbon

A racemic mixture is formed when a molecule with a chiral center is produced. A chiral center is a carbon atom bonded to four different groups.

- Examine Neopentane

Neopentane (2,2-dimethylpropane) has no chiral center upon monochlorination because all possible chlorine substitution sites are symmetrical.

- Examine -Butane

n-Butane, when monochlorinated, does not produce a chiral carbon since the chlorination happens at any of the primary hydrogens and produces symmetrical molecules.

- Examine 2,3-Dimethylbutane

Monochlorination of 2,3-dimethylbutane at either of the central carbons (C2 or C3) results in creating a chiral center as they will attach to four different groups thus creating a racemic mixture.

- Examine 2,2,3,3-Tetramethylbutane

2,2,3,3-Tetramethylbutane has no hydrogen atoms to replace with chlorine, so monochlorination does not apply.

- Conclusion

Based on the examination, 2,3-dimethylbutane is the only compound that upon monochlorination produces a racemic mixture due to the formation of a chiral center.

Key concepts

racemic mixture

A racemic mixture is a blend of two enantiomers in exactly equal amounts. Enantiomers are mirror-image forms of a chiral molecule. When an organic reaction produces a chiral product, and the product is an equal mix of both enantiomers, a racemic mixture is formed. It's important since it affects how the compound behaves chemically and biologically. For example, in our exercise, the formation of a racemic mixture indicates the creation of a chiral center, essential for understanding chemical reactivity and properties.

chiral center

A chiral center is a specific type of carbon atom in organic molecules. It is bonded to four different groups, making it asymmetric. This means the molecule is non-superimposable on its mirror image, like left and right hands. The chiral center is crucial in organic chemistry as it influences the molecule's interactions. In the given exercise, examining if monochlorination creates a chiral center helps determine if a racemic mixture is produced. The identification of a chiral center in 2,3-dimethylbutane upon monochlorination was key to solving the problem.

organic chemistry

Organic chemistry studies carbon-containing compounds. It's a vast field encompassing everything from hydrocarbons like alkanes to complex proteins and DNA. The focus is on understanding how carbon atoms bond with other elements to form various structures. This includes reactions like monochlorination, where one hydrogen atom in an alkane is replaced with a chlorine atom. By studying such reactions, we learn about the properties and behaviors of organic molecules. The exercise demonstrated this by exploring how different alkanes respond to monochlorination and if they create racemic mixtures.

hydrocarbons

Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon atoms. They are the simplest form of organic molecules and serve as the foundation for more complex compounds. There are several types of hydrocarbons, including alkanes, which are saturated hydrocarbons with single bonds. In the exercise, we deal with different alkanes like neopentane, n-butane, 2,3-dimethylbutane, and 2,2,3,3-tetramethylbutane. Understanding their structure helps us determine their behavior in reactions like monochlorination and the potential formation of chiral centers and racemic mixtures.