Question

Give condensed structures corresponding to the following IUPAC names: (a) cis-2-Hexene (b) 2 -Methyl-3-hexene (c) 2 -Methyl- 1,3 -butadiene

Short answer

(a) CH₃CH=CHCH₂CH₂CH₃; (b) CH₃CH(CH₃)CH=CHCH₂CH₃; (c) CH₂=C(CH₃)CH=CH₂.

Step-by-step solution

Analyze the IUPAC Name for Part (a)

The name 'cis-2-Hexene' indicates that this is an alkene with a total of six carbon atoms. The prefix 'cis' suggests that the substituents on either side of the double bond at carbon 2 are on the same side.

Draw the Structural Formula for cis-2-Hexene

Start with the longest chain of six carbon atoms. Place a double bond between the second and third carbon atoms. Ensure both substituents on the double-bonded carbons are on the same side to denote the 'cis' configuration.

Convert to Condensed Structural Formula for cis-2-Hexene

For cis-2-hexene, the condensed structural formula is represented as: CH₃CH=CHCH₂CH₂CH₃.

Analyze the IUPAC Name for Part (b)

The name '2-Methyl-3-hexene' means there is a six-carbon alkene chain with a double bond starting at carbon 3 and a methyl group attached to carbon 2.

Draw the Structural Formula for 2-Methyl-3-Hexene

Draw a six-carbon chain and place a double bond between carbon 3 and carbon 4. Add a methyl group (CH₃) to the second carbon.

Convert to Condensed Structural Formula for 2-Methyl-3-Hexene

The condensed structural formula is: CH₃CH(CH₃)CH=CHCH₂CH₃.

Analyze the IUPAC Name for Part (c)

The name '2-Methyl-1,3-butadiene' indicates a four-carbon chain with two double bonds, one at carbon 1 and another at carbon 3, and a methyl group attached to carbon 2.

Draw the Structural Formula for 2-Methyl-1,3-butadiene

Construct a four-carbon chain, position double bonds between carbon 1-2 and carbon 3-4, and attach a methyl group to carbon 2.

Convert to Condensed Structural Formula for 2-Methyl-1,3-butadiene

The condensed structural formula is: CH₂=C(CH₃)CH=CH₂.

Key concepts

Organic Chemistry

Organic chemistry is all about studying carbon-containing compounds. It focuses on the structure, properties, reactions, and preparation of carbon-based molecules, which can be very complex. Most organic compounds contain hydrogen, oxygen, nitrogen, and other elements, but carbon is always the key player.

Carbon's unique ability to form four covalent bonds makes it incredibly versatile. It can create long chains, branching structures, and rings, leading to an endless variety of chemical compounds. This facet of carbon chemistry allows for the formation of the vast array of organic compounds that we see today, from simple molecules like methane to complex proteins.

Understanding organic chemistry is foundational, as it connects to many fields including biochemistry, medicine, and materials science. It's crucial for designing drugs, creating better materials, and understanding the chemistry of life itself.

Alkenes

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond. This double bond is a defining feature, giving alkenes the general formula \(C_nH_{2n}\), where n is the number of carbon atoms.

The presence of a double bond not only alters the chemical reactivity of these molecules but also their geometrical shape compared to single-bonded alkanes. Alkenes are unsaturated hydrocarbons, meaning they have fewer hydrogen atoms than their alkane counterparts. This results from the presence of the double bond, allowing them to react with other substances more readily.
Alkenes are the basic building blocks in the synthesis of many other compounds, like plastics or alcohols, through reactions like polymerization and hydration. Their double bonds make them reactive and versatile intermediates in many chemical reactions.

IUPAC Nomenclature

The IUPAC (International Union of Pure and Applied Chemistry) nomenclature is a standardized method for naming chemical compounds to ensure that each has a unique and universally accepted name. This system eliminates confusion and allows chemists across the globe to communicate effectively about these compounds.

Each part of an IUPAC name has a specific meaning:

• The root indicates the number of carbon atoms in the longest continuous chain.
• The suffix denotes the type of carbon-carbon bonds present, like -ene for double bonds.
• Prefixes and locants describe the positions of functional groups and other substituents.

For example, in "2-methyl-3-hexene," "hexene" refers to a six-carbon chain with a double bond, "methyl" specifies a one-carbon branch, and "3" indicates the location of the double bond starting point. Understanding these rules helps in constructing the structural formulas efficiently.

Cis-Trans Isomerism

Cis-trans isomerism is a subtype of stereoisomerism found in compounds with double bonds. It arises because double bonds prevent free rotation around the bond, unlike single bonds, which can freely rotate.

When two identical atoms or groups are attached to each end of the double-bonded carbon atoms, they can be on the same side, forming a "cis" isomer, or on opposite sides, forming a "trans" isomer. These different arrangements result in distinct physical and chemical properties.

This type of isomerism is important in a variety of fields:

• In organic chemistry, it influences boiling points and solubilities.
• In biology, it can affect the function of biomolecules like fatty acids and retinoids.

Coming back to cis-2-hexene: here, the identical groups on either side of the double bond are on the same side, denoting the cis configuration, which influences how the molecule behaves in chemical reactions.