Question

Draw structures for the following compounds: (a) \((3 R, 4 S)\)-dichlorohexane (d) iodoethene (b) 3-bromocyclohexene (e) 1,1 -dichlorocyclopropane (c) \((Z)\)-1-bromo-1-butene

Short answer

Draw the structures of hexane, cyclohexene, butene, ethene, and cyclopropane with specified substituents and configurations.

Step-by-step solution

- Draw the skeleton of each molecule

For each compound, start by drawing the basic skeleton. (a) Hexane has 6 carbon atoms in a straight chain. (b) Cyclohexene is a six-membered ring with one double bond. (c) 1-butene has 4 carbons in a straight chain with a double bond between C-1 and C-2. (d) Ethene has 2 carbon atoms with a double bond. (e) Cyclopropane is a three-membered ring.

- Add substituents at the specified positions

Add the given substituents to each skeleton. (a) Add chlorine atoms at C-3 and C-4, considering R and S configuration. (b) Bromine at C-3 of cyclohexene. (c) Bromine at C-1 of 1-butene. (d) Iodine at one of the carbon atoms in ethene. (e) Two chlorine atoms at C-1 of cyclopropane.

- Apply stereochemistry and double bond configuration

Carefully apply the stereochemistry where needed. (a) For \(3R, 4S\)-dichlorohexane, position the chlorine atoms with the correct R and S configurations. (c) \(Z\)-1-bromo-1-butene means that the highest priority groups on each carbon of the double bond are on the same side.

- Verify the structures

Ensure that each structure is correct by verifying the number of bonds, the placement of substituents, and the stereochemistry.

Key concepts

stereochemistry

Stereochemistry is the study of the spatial arrangement of atoms in molecules and how they affect the physical and chemical properties of those molecules. Certain molecules can exist in forms that are mirror images of each other. These are known as enantiomers. They have the same molecular formula but different 3D structures. For instance, the compound (3R, 4S)-dichlorohexane has specific spatial arrangements that must be considered. Here, 'R' and 'S' denote the configurations of the chiral centers, determined by the Cahn-Ingold-Prelog priority rules.
In enantiomers:

• 'R' (rectus) means the configuration is clockwise from the highest priority substituent.
• 'S' (sinister) means the configuration is counterclockwise.

This spatial configuration can significantly affect a molecule's reactivity and interaction with biological systems. When drawing or interpreting stereochemical structures, always double-check the 3D spatial arrangement on paper or using models.

alkenes

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond, denoted by C=C. Units of unsaturation like these introduce a level of complexity into molecular structures. A key feature of alkenes is their geometric (cis/trans or E/Z) isomerism due to restricted rotation around the double bond.
For example:

• In (Z)-1-bromo-1-butene, the Z designation means 'zusammen' or 'together' in German. It indicates that the highest priority substituents on each carbon involved in the double bond are on the same side.
• Conversely, 'E' (entgegen) would mean they are on opposite sides.

These geometric distinctions become crucial when predicting chemical reactivity and physical properties like boiling points and densities.

alkanes

Alkanes are the simplest family of hydrocarbons, consisting only of single bonds between carbon atoms and having the general formula C_nH_{2n+2}. They are often referred to as saturated hydrocarbons.
When naming and drawing alkanes:

• Each carbon atom forms four single covalent bonds with hydrogen atoms or other carbon atoms.
• In the compound (3R, 4S)-dichlorohexane, hexane refers to a six-carbon alkane, where two carbon atoms have chlorine substituents.

Due to their simplicity, alkanes often serve as a fundamental building block in organic chemistry, helping understand more complex structures and reactivities.

functional groups

Functional groups are specific groups of atoms within molecules that have characteristic properties and reactivities. They play a significant role in organic chemistry nomenclature and classification.
For example:

• Bromo (–Br) and chloro (–Cl) groups are types of halogen functional groups.
• The presence of a functional group can drastically alter a molecule's reactivity. For example, attaching a bromine to 1-butene results in 1-bromo-1-butene, introducing new reaction possibilities.
• Iodine, as seen in iodoethene, is another halogen that confers particular characteristics, such as increased reactivity towards nucleophiles.

Recognizing and understanding functional groups helps predict and explain how molecules behave in different chemical reactions.

cyclic compounds

Cyclic compounds contain ring structures formed by two or more carbon atoms. These rings introduce new layers of complexity due to torsional strain, angle strain, and potentially unique spatial characteristics.
Some key types include:

• Cyclohexene: A six-membered ring with one double bond, as in 3-bromocyclohexene. The double bond introduces variations in reactivity and angle strain.
• Cyclopropane: A three-membered ring seen in 1,1-dichlorocyclopropane. This ring has significant angle strain due to its small size, resulting in unique reactivity patterns.

Cyclic compounds are ubiquitous in natural and synthetic chemistry, and understanding their properties is essential for advanced applications in pharmaceuticals, materials science, and more.