Question

Draw a structural formula for each of the following compounds. (a) 3 -isopropyloctane; (b) 2 -chloro- 3 -methylpentane; (c) 2 -pentene; (d) dipropyl ether.

Short answer

The drawn structures of the compounds are: (a) 3 -isopropyloctane: An octane chain with an isopropyl group attached to the third carbon. (b) 2 -chloro- 3 -methylpentane: A pentane chain with a chlorine atom attached to the second carbon and a methyl group attached to the third carbon. (c) 2 -pentene: A pentene chain with a double bond between the second and third carbons. (d) Dipropyl ether: Two propyl groups attached to an oxygen atom.

Step-by-step solution

Understand the nomenclature

In organic chemistry nomenclature, the first part of the name generally speaks about the parent hydrocarbon chain. The prefixes denote the position of the groups attached to the parent chain. For example, '3-isopropyloctane' means that on the third carbon of the octane chain an isopropyl group is attached

Draw the parent chain

Draw the main or parent hydrocarbon chain. For instance, octane is an eight-carbon chain. This will form the 'backbone' of our structure.

Attach the groups to the parent chain

Now it is time to attach the groups to our main chain as indicated by the nomenclature. In our example, attach an isopropyl group to the third carbon of the octane chain.

Repeat steps 2 and 3 for other compounds

Repeat the previous steps for other compounds: '2 -chloro- 3 -methylpentane,' '2 -pentene,' 'dipropyl ether.' Understand the nomenclature before starting to draw.

Revise the drawn structures

After drawing the structures, revise them to ensure that they match with the given names and there are no loose bonds.

Key concepts

Organic Chemistry Nomenclature

Organic chemistry nomenclature is a systematic way of naming chemical compounds. In these exercises, the names given hold the key to understanding the specific structure of the molecule. The name reveals the number of carbon atoms and any additional groups that are bonded to the hydrocarbon chain.
For instance, in "3-isopropyloctane," the "octane" portion tells us that the main chain has eight carbon atoms. "Isopropyl" indicates a side group, composed of three carbon atoms arranged in a branched form, that is attached to the third carbon atom of the primary chain. Detailed attention to these prefixes and suffixes in the nomenclature helps you build the correct molecular structure.
Nomenclature can also indicate functional groups. For example, in "2-chloro-3-methylpentane," "chloro" represents a chlorine atom, and "methyl" is a one-carbon side group. These are attached to the corresponding numbered carbon atoms in the main chain.

Hydrocarbon Chains

Hydrocarbon chains are the backbone of organic molecules, made solely of carbon and hydrogen atoms. In structural formulas, the hydrocarbon chain provides the essential framework upon which other atoms or groups are attached.
For example, in the exercise of "3-isopropyloctane," octane is a simple hydrocarbon made up of eight carbon atoms in a continuous chain. Each carbon is saturated, meaning all its bonds are filled with hydrogen atoms, except where other groups attach.
The hydrocarbon chain length and structure, whether linear or branched, affects the physical and chemical properties of the molecule. In the case of alkenes like "2-pentene," a double bond introduces an unsaturated aspect, altering the chemical behavior and geometry of the molecule.

Functional Groups

Functional groups are specific groups of atoms within molecules that have characteristic properties regardless of the other atoms present in a molecule. They play a crucial role in the chemical behavior of organic compounds.
In the exercise, "2-chloro-3-methylpentane" includes a "chloro" group, a halogen that significantly alters the molecule's reactivity compared to a purely hydrocarbon chain.
For "dipropyl ether," the functional group is an ether, which consists of an oxygen atom connected to two alkyl groups like propyl. This presence of an ether group influences factors like boiling point and solubility. Recognizing and understanding the impact of functional groups is vital in predicting how organic molecules will interact in chemical reactions.

Chemical Structure Drawing

Chemical structure drawing is the art of creating a visual representation of a molecule, showing how atoms are connected through bonds. It's an essential skill in organic chemistry.
Start by drawing the main hydrocarbon chain as a straight or branched line, representing the backbone's carbon atoms. Then, add the side groups or functional groups at the appropriate positions as dictated by the molecule's name.
Use single, double, or triple lines to represent bonds between carbon atoms, paying special attention to the geometry. For example, ensure that double-bonded carbons, as in "2-pentene," appear flat and connected by a double line.
Finally, inspect your diagrams to ensure that each atom forms the correct number of bonds, typically four for carbon, and none are left unattached unless specified. This careful depiction aids in understanding the 3D shape and reactivity of the molecule.