Problem 11 - Chemistry The Central Science In Si Units

Question

For each of the following hydrocarbons, state how many carbon atoms are in each molecule: (a) \(t\) -butanol (b) propanone (c) 2-ethylpropane (d) cyclohexane (e) ethane

Step-by-Step Solution

Answer

(a) 4 carbons, (b) 3 carbons, (c) 5 carbons, (d) 6 carbons, (e) 2 carbons.

Step 1 - Understanding Hydrocarbon Naming

Hydrocarbons are named following IUPAC nomenclature. The name provides information about the number and arrangement of carbon atoms. Prefixes like 'meth-', 'eth-', 'prop-', 'but-' indicate 1, 2, 3, and 4 carbons respectively, while suffixes such as '-ane', '-ene', and cyclic structures give insight into the molecular structure.

Step 2 - Analyzing 't-butanol'

The 'but-' prefix indicates 4 carbon atoms. The 't' signifies tertiary, meaning the alcohol group (-OH) is attached to a carbon that is attached to three other carbons, but this does not change the initial carbon count derived from 'but'.

Step 3 - Analyzing 'propanone'

The 'prop-' prefix indicates 3 carbon atoms. 'One' refers to a ketone group (C=O), but does not add or change carbon numbers.

Step 4 - Analyzing '2-ethylpropane'

The 'propane' base indicates 3 carbon atoms. The 'ethyl' group adds 2 more carbons. Therefore, 3 (from propane) + 2 (from ethyl) = 5 carbon atoms.

Step 5 - Analyzing 'cyclohexane'

The 'hex-' in 'cyclohexane' indicates 6 carbon atoms arranged in a ring structure.

Step 6 - Analyzing 'ethane'

The 'eth-' prefix indicates 2 carbon atoms. The '-ane' suffix specifies it as an alkane, but does not alter the number of carbons.

Key Concepts

Understanding Hydrocarbons

Hydrocarbons form the basis of organic chemistry, consisting solely of carbon and hydrogen atoms. They can be simple molecules like ethane (C₂H₆) or more complex formations. The way these atoms are arranged and bonded determines the hydrocarbon's properties and classification:

• Saturated hydrocarbons, or alkanes, have single bonds and follow the formula CₙH₂ₙ₊₂.
• Unsaturated hydrocarbons include alkenes, with the formula CₙH₂ₙ, featuring at least one carbon-carbon double bond.
• Alkynes have a triple bond, following the formula CₙH₂ₙ₋₂.

Understanding hydrocarbons is fundamental because they are the building blocks of many organic molecules.
IUPAC nomenclature helps identify the number of carbon atoms and how they are arranged in a molecule, making it easier to understand their structure and characteristics.

The Role of Carbon Atoms in Hydrocarbons

Carbon atoms are essential in forming the backbone of hydrocarbons. This is due to carbon's ability to form four covalent bonds, allowing it to create various complex structures. These structures can be:

• Linear chains: where carbon atoms are connected in a straight line.
• Branched chains: involving carbon backbones with side carbon branches, altering the molecule's properties.
• Cyclic rings: where carbon atoms form closed ring structures, influencing the molecule's stability and reactivity.

The unique versatility of carbon makes it possible for countless organic compounds to exist, each with different traits. In IUPAC naming, prefixes and suffixes indicate the number of carbon atoms and the type of bonds present, giving clues to the molecule's structure.

The Basics of Organic Chemistry

Organic chemistry focuses on carbon-containing compounds, primarily hydrocarbons and their derivatives. The study extends beyond simple structures to those with various functional groups, altering their chemical behavior.  Knowledge of organic chemistry enables us to understand biological processes and synthesize useful products like medicines and plastics.

• Hydrocarbons are organized based on their structure and function.
• Functional groups, like alcohols and ketones, add diversity in reactivity and properties.

The discipline relies on recognizing patterns in molecule structures and the IUPAC naming system to systematize the vast array of organic compounds.

Functional Groups: Defining Organic Molecules

Functional groups are specific atoms or clusters of atoms within molecules responsible for characteristic reactions. They modify hydrocarbons by introducing elements like oxygen, nitrogen, or halogens, thus influencing the compound's physical and chemical properties. Some common functional groups include:

• Alcohols (-OH): introduce polarity, increasing solubility in water.
• Ketones (C=O): affect the molecule's reactivity, participating in reduction and oxidation reactions.
• Carboxylic acids (-COOH): are acidic due to the ability to donate a hydrogen ion.

Understanding functional groups is crucial because they play a key role in chemical synthesis and biological function. In the IUPAC naming system, they are often indicated by specific suffixes or prefixes, providing insights into the molecule's properties and potential reactivity.