Question

For each category of compounds the minimum number of carbons required for optical isomerism to be possible is given. Find the correct match (es). (a) Alkane - 7 (b) Alkene - 6 (c) Alkyl halide \(-4\) (d) Alkadiene - 7

Short answer

(a) Alkane - 7, (b) Alkene - 6, (c) Alkyl halide - 4, (d) Alkadiene - 7 are correct matches.

Step-by-step solution

Understand Optical Isomerism

Optical isomerism occurs when a compound has chiral centers, which usually are carbon atoms bonded to four different groups. A compound must have at least one such chiral center to exhibit optical isomerism.

Determine Minimum Carbon for Alkanes

An alkane requires at least 7 carbons to form a chiral center, as with fewer carbons it's not possible to have four distinct substituents on a carbon. Hence, part (a) is correct.

Check Minimum Carbon for Alkenes

For an alkene, a chiral center can be present with 6 carbons. For instance, in substituted alkenes, the presence of different groups can lead to a chiral carbon. Thus, part (b) is correct.

Check Minimum Carbon for Alkyl Halides

Alkyl halides can have an optical isomer with a minimum of 4 carbons. A simple example is 2-chlorobutane, where the second carbon can be chiral. Therefore, part (c) is correct (-4 was likely a typographical mistake; the correct matching text is "4").

Evaluate Alkadienes

Alkadienes have a similar requirement as alkanes. They need at least 7 carbon atoms to ensure the presence of a chiral center due to similar substituent arrangements possible with double bonds. Hence, part (d) is correct.

Key concepts

Chiral Center

In organic chemistry, a chiral center plays a crucial role in determining the optical isomerism of a molecule. It is essentially a carbon atom bonded to four different substituents. This unique arrangement allows the molecule to exist in two non-superimposable mirror images, much like your left and right hands. These mirror images are known as enantiomers, and they rotate plane-polarized light in different directions – one clockwise and the other counterclockwise.

• Enantiomers have the same physical properties, such as melting and boiling points, but differ in their optical activity.
• Identifying chiral centers is key to predicting the optical isomerism in compounds.

The presence or absence of chiral centers is an important factor when studying the optical properties of organic substances.

Minimum Carbon Atoms

The concept of minimum carbon atoms comes into play when determining how many carbon atoms are needed for a particular compound to exhibit optical isomerism. This number varies depending on the type of organic compound.
For a carbon to act as a chiral center in a simple organic molecule, it needs at least four different substituents. Hence, certain classes of molecules require a minimum number of carbon atoms to achieve the variegation of substituents needed for chirality.

• Alkanes typically need at least seven carbon atoms.
• Alkenes can often form with six carbon atoms.
• Alkyl halides, on the other hand, may require only four carbon atoms for a chiral center.

Understanding the minimum carbon atoms necessary helps in the study and synthesis of optically active molecules.

Organic Compounds

Organic compounds are primarily made up of carbon atoms and are the building blocks of all living organisms. They encompass a wide range of molecules that vary in complexity and functionality. Organic chemistry is centered around the study of these compounds.
The classification of organic compounds based on their structures and functional groups is essential for understanding their chemical properties.

• Examples of organic compounds include alkanes, alkenes, alkyl halides, and alkadienes.
• Each class of compounds has unique characteristics that affect their reactivity and interaction with other substances.

Organic chemistry explores how these compounds can be synthesized, altered, and utilized in various applications, such as pharmaceuticals and materials science.

Alkanes

Alkanes are a class of organic compounds that consist entirely of single-bonded carbon and hydrogen atoms. They are saturated hydrocarbons because they contain the maximum number of hydrogen atoms possible on their carbon chains.

• They have a general formula of C\(_n\)H\(_{2n+2}\).
• Alkanes are found in nature in various forms, such as methane, ethane, and propane.

Optical isomerism in alkanes requires a minimum of seven carbon atoms to form chiral centers. This is because alkanes with fewer carbon atoms lack sufficient diversity in their substituents to create chirality.

Alkenes

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond, making them unsaturated. This double bond is not only chemically reactive but also allows for the formation of geometric isomers.
The presence of double bonds means that alkenes can have a chiral center with just six carbon atoms, especially when they are substituted with different groups.

• Common examples of alkenes include ethene (ethylene) and propene (propylene).
• Their general formula is C\(_n\)H\(_{2n}\).

Chirality in alkenes contributes to their complex reactions and interactions, making them an important focus of study in organic chemistry.

Alkyl Halides

Alkyl halides, also known as haloalkanes, are compounds derived from alkanes where one or more hydrogen atoms are replaced by halogen atoms such as fluorine, chlorine, bromine, or iodine. These substances are incredibly versatile and reactive due to the presence of these halogens.
Optical isomerism in alkyl halides can occur with as few as four carbon atoms, as seen in compounds like 2-chlorobutane.

• The presence of a halogen alters the compound's reactivity significantly, making them useful in various chemical reactions.
• Alkyl halides serve vital roles in the field of pharmaceuticals and agrochemicals.

Their ability to form chiral centers in such short carbon chains highlights their significance in stereochemical studies.

Alkadienes

Alkadienes are hydrocarbons characterized by having two double bonds. These double bonds increase the possibility of forming structural isomers and influence the molecule's overall stability and reactivity.
Alkadienes need at least seven carbon atoms to potentially have a chiral center capable of optical isomerism, akin to alkanes.

• They exhibit a broad range of chemical behavior due to their multiple bonds.
• Such compounds are often involved in polymer industries to create synthetic materials.

The configuration of alkadienes greatly affects their functionality and application in various chemical processes.