Question

Give the structural formulas of the following compounds. (a) \(2,2,4\)-trimethylpentane (b) 3-ethyl-2-pentene (c) 1,3 -butadiene (d) cyclobutane (e) chlorobenzene

Short answer

a) \(2,2,4\)-trimethylpentane is a five carbon chain with two methyl groups on the second carbon and one methyl group on the fourth carbon. \n b) 3-ethyl-2-pentene contains a five carbon chain with a double bond on the second carbon and an ethyl group on the third. \n c) 1,3 -butadiene represents a four carbon chain with two double bonds; one each between the first and second, third and fourth carbon atoms. \n d) cyclobutane is a closed loop of four carbon atoms. \n e) chlorobenzene is a benzene ring with a chlorine substituent.

Step-by-step solution

Structural formula of \(2,2,4\)-trimethylpentane

In this name, 'pentane' indicates a chain of five carbon atoms. 'Trimethyl' means there are three methyl (\(-CH3\)) groups, and '2,2,4-' indicates their positions. Two methyl groups are attached to the second carbon atom, and one methyl group is attached to the fourth carbon atom from one end of the carbon chain.

Structural formula of 3-ethyl-2-pentene

Here, 'pentene' suggests a five-carbon chain with a double bond. The number '2' before pentene indicates that the double bond starts from the second carbon atom. 'Ethyl' represents a \(-CH2CH3\) group, and '3-' signifies it is connected to the third carbon of the carbon chain.

Structural formula of 1,3 -butadiene

The term 'butadiene' stands for a four-carbon atom chain with two double bonds. The numbers '1,3' mean the double bonds are between the first and second, and third and fourth carbon atoms.

Structural formula of cyclobutane

'Cyclobutane' suggests a closed loop or a cyclic structure of four carbon atoms. As there are no other groups or multiple bonds mentioned, it's a simple cyclic structure with carbon atoms linked by single bonds.

Structural formula of chlorobenzene

In the name 'chlorobenzene', 'benzene' means a six-carbon cyclic structure with alternate double bonds. 'Chloro' indicates there's a chlorine atom as a substituent. Without any numerical indication, it can be attached at any carbon in the benzene ring.

Key concepts

IUPAC Nomenclature

Understanding the nomenclature of organic compounds is crucial for students of organic chemistry. The International Union of Pure and Applied Chemistry (IUPAC) developed a systematic method for naming organic chemical compounds. This method ensures that each compound has a unique and unambiguous name. The process starts with identifying the longest continuous chain of carbon atoms, which forms the base name of the compound, like 'pentane' in '2,2,4-trimethylpentane'.

Addition of prefixes and suffixes elaborates on the types and positions of different substituents or functional groups attached to that chain. For example, in '3-ethyl-2-pentene', 'ethyl' is a prefix denoting an ethyl group, while 'ene' is a suffix indicating the presence of a double bond. Numbers like '3-' and '2-' specify the exact carbon atoms these features are attached to, counting from the end of the chain nearest to the first substituent encountered. Learning IUPAC nomenclature is essential as it provides a clear and standardized system for referring to complex organic compounds.

Organic Chemistry

Organic chemistry is the study of carbon-containing compounds, their structure, properties, and reactions. Carbon's unique ability to form strong covalent bonds with other elements and itself allows for an immense variety of compounds, as seen in the textbook examples.

In organic molecules, carbon atoms can be arranged in chains, branched chains, or rings, and they can be saturated or unsaturated with single, double, or triple bonds, as demonstrated by compounds ranging from 'cyclobutane' to '1,3-butadiene'. The diversity of molecular structures results in different physical and chemical behaviors, which are key to understanding how organic compounds interact in various chemical reactions and biological systems.

Alkenes and Alkynes

Alkenes and alkynes are categories of hydrocarbons characterized by the presence of double and triple carbon-carbon bonds, respectively. These unsaturated bonds confer unique reactivity patterns to such compounds.

For instance, '3-ethyl-2-pentene' features an alkene with a double bond between the second and third carbon atoms. The term 'ene' indicates this double bond. Likewise, '1,3-butadiene', while still considered an alkene, contains two double bonds, making it a diene. Alkynes, though not represented in the given exercise, would have names ending in 'yne' and feature a carbon-carbon triple bond. The presence of multiple or triple bonds makes alkenes and alkynes more chemically reactive compared to alkanes, which only contain single bonds and are saturated hydrocarbons.

Aromatic Compounds

Aromatic compounds play a significant role in organic chemistry due to their stable and unique ring-based structures. They consist of cyclic molecules with a planar geometry and delocalized electrons obeying Huckel's rule.

'Chlorobenzene' is an example of an aromatic compound, where 'benzene' signifies a six-carbon ring with alternating double bonds – a structure known for its exceptional stability. A 'chloro' substituent on the benzene ring implies the presence of a chlorine atom. Aromatic compounds such as chlorobenzene have distinct chemical properties, including a tendency to undergo substitution reactions rather than the addition reactions more common with alkenes and alkynes. This stability and distinctive reactivity make aromatic compounds a fundamental topic in the study of organic chemistry.