Question

Which classes of hydrocarbon are unsaturated?

Short answer

Unsaturated hydrocarbons are alkenes and alkynes.

Step-by-step solution

Understanding Hydrocarbon Saturation

Hydrocarbons can be classified as saturated or unsaturated based on the type of bonds between their carbon atoms. Saturated hydrocarbons have only single bonds (alkanes), while unsaturated hydrocarbons contain double or triple bonds (alkenes or alkynes).

Identifying Unsaturated Hydrocarbons

To determine which hydrocarbons are unsaturated, we need to identify those that contain either double or triple carbon-carbon bonds. These bonds allow the hydrocarbon to potentially add more hydrogen atoms, unlike saturated hydrocarbons that have the maximum number of hydrogen atoms for each carbon.

Classes of Unsaturated Hydrocarbons

The primary classes of unsaturated hydrocarbons are alkenes and alkynes. Alkenes have at least one carbon-carbon double bond, whereas alkynes have at least one carbon-carbon triple bond.

Conclusion

Based on the presence of double and triple bonds, alkenes and alkynes are considered unsaturated hydrocarbons. These bonds distinguish them from alkanes, which are saturated hydrocarbons.

Key concepts

Saturated Hydrocarbons

Saturated hydrocarbons, also known as alkanes, are a class of hydrocarbons in which all the carbon-carbon bonds are single covalent bonds. This distinctly strong type of bonding occurs when two carbon atoms share two electrons, with the surrounding hydrogen atoms each sharing another electron with the carbon to complete the molecule's structure. Due to the saturation of all carbon atoms in relation to hydrogen, these molecules are saturated with hydrogen atoms.

A few key characteristics of saturated hydrocarbons include:

• They are generally less reactive because the single bonds make the structure more stable.
• They have a straight or branched-chain structure, leading to various isomers.
• Commonly found in natural resources like petroleum and natural gas.

You'll often encounter alkanes during studies of fossil fuels and their combustion properties. Understanding these can also aid in grasping the chemistry behind energy production.

Alkenes

Alkenes are a fascinating class of unsaturated hydrocarbons. They possess at least one carbon-carbon double bond, which introduces an element of flexibility in terms of chemical reactivity. The double bond in alkenes consists of a sigma bond and a pi bond, making the bond stronger and more rigid than a single covalent bond, yet allowing geometric isomerism to occur.

Some notable properties and reactions of alkenes include:

• Greater reactivity than alkanes due to the presence of the double bond.
• They undergo addition reactions, where new atoms can be added across the double bond.
• The ability to form polymers, which are large molecules, used extensively in plastic production.

In industrial applications, alkenes are vital. For example, ethene (ethylene) is a primary molecule in the production of polyethylene plastics. Due to their varied applications and reactive nature, alkenes are a central topic in organic chemistry.

Alkynes

Alkynes, another intriguing group of unsaturated hydrocarbons, are characterized by having at least one carbon-carbon triple bond. This triple bond consists of one sigma bond and two pi bonds, making alkynes even more reactive than alkenes. The linear geometry of the triple bonded atoms gives alkynes a distinctive structural feature.

Important characteristics and uses of alkynes include:

• High reactivity, with the ability to undergo a variety of chemical reactions.
• Used as starting materials in complex organic synthesis due to their versatile nature.
• Acetylene, the simplest alkyne, is commonly used in welding torches because it burns with an intensely hot flame.

Alkynes offer a great depth of study due to their potential in synthetic applications and are pivotal in creating complex organic chemicals. Their unique bond structure provides endless opportunities for chemical innovation.