Name: naming alkane chains and substituents
Uploaded: 2023-04-30T18:28:32.000Z
Duration: 2 min 22 s
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Matter and its Interactions

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Nomenclature of Alkanes

The IUPAC names of unbranched alkanes include a stem to signify the length of the carbon chain and the suffix &#8220;ane&#8221; to identify the compounds as alkanes.
For example, the five-carbon alkane with the stem &#39;pent&#39; and the suffix &#39;ane&#39; acquires the name &#8212; pentane.
A substituent formed from an alkane is called an alkyl group. For instance, removing one of the terminal hydrogen atoms from pentane gives the pentyl group.
The IUPAC names of branched alkanes have three parts: parent, substituent, and locant. The parent includes a stem and the suffix, and the locant indicates the substituent&#8217;s location on the parent.
The parent is identified as the longest continuous chain of carbon atoms. If two or more chains have the same number of carbon atoms, the chain with the greater number of branching points becomes the parent.
Locants are assigned by numbering the carbon atoms of the parent chain.
In the case of a single substituent, numbering begins from the end of the chain that assigns the lower value to the branching point. Thus, the correct name is 3-methylheptane.
A hyphen separates the number and the substituent.
If a molecule has multiple identical substituents, the numbers are assigned su

nomenclature of alkanes

In the late 19th-century, the number of new chemical compounds discovered increased tremendously. Hence, the necessity arose to develop a naming system for the systematic nomenclature of these newly discovered compounds. IUPAC (International Union for Pure and Applied Chemistry), established in 1919, sets rules for the nomenclature.
The alkane nomenclature considers the length of the carbon chain, the number, and the location of the substituent to arrive at its systematic name. The IUPAC nomenclature is done stepwise, and it is universally acceptable. The first step is to determine and name the longest carbon chain, also known as the parent chain. For example, an alkane having the longest carbon chain of five carbon atoms gets the parent name pentane.
The second step is to identify and name the substituents. The name of the substituent, known as a prefix, is positioned before the parent name. For example, a pentane chain having a methyl substituent gets the name methylpentane. The third step is to determine the location of the substituent by numbering the longest carbon chain. The numbering is done in such a way that the carbon on which the substituent is situated gets the lowest number. Thus, the methyl group positioned on the second carbon will obtain the name 2-methyl pentane&#160;and not 4-methyl pentane. If more than one identical or non-identical substituents are present, additional IUPAC rules apply.

In the late 19th-century, the number of new chemical compounds discovered increased tremendously. Hence, the necessity arose to develop a naming system ...

Education

JoVE Core

Organic Chemistry

Unit 1

Alkanes and Cycloalkanes

KEY TERMS AND CONCEPTS

naming alkane chains and substituents

Alkane names follow IUPAC rules, a system used to name organic compounds in a clear and standard way. These rules became important in the late 19th century as new chemical compounds were discovered at a fast pace. IUPAC, the International Union for Pure and Applied Chemistry, was established in 1919 to set these naming rules.

The naming process for alkanes depends on the length of the carbon chain, the number of substituents, and where those substituents are placed. The first step is to find the longest carbon chain. This chain is called the parent chain. A chain with five carbon atoms, for example, is named pentane.

The next step is to identify the substituents. A substituent is a side group attached to the parent chain. Its name is written as a prefix before the parent name. If a pentane chain has a methyl substituent, the name becomes methylpentane.

The final step is to number the parent chain so the substituent gets the lowest possible number. If a methyl group is on the second carbon, the name is 2-methylpentane, not 4-methylpentane. When more than one identical or different substituent is present, additional IUPAC rules are used.

Naming Alkane Chains and Substituents

structure of alkanes

Alkane Bonding and Formula Patterns

Alkanes are the simplest hydrocarbons, and their structure starts with carbon-carbon bond formation. That idea helped shape organic chemistry, as August Kekulé and Archibald Scott Couper independently proposed carbon chain formation. Hydrocarbons are organic compounds made only of carbon and hydrogen. Based on the bond order between carbon atoms, hydrocarbons are classified as alkanes, alkenes, and alkynes. Alkanes contain sp3 hybrid carbon atoms. These carbons form sigma bonds with other sp3...

constitutional isomers of alkanes

Alkane Branching and Isomer Counts

Alkanes can form constitutional isomers, which are compounds with the same molecular formula but different structural formulas. This idea is called constitutional isomerism. It becomes important for alkanes with four or more carbons, because they can have more than one structure with the same formula. A straight-chain alkane is named with the prefix n, so the linear form of pentane is n-pentane. Branched isomers use prefixes such as iso and neo. Pentane has two branched isomers, iso-pentane...

Alkane names follow IUPAC rules, a system used to name organic compounds in a clear and standard way. These rules became important in the late 19th century as new chemical compounds were discovered at a fast pace. IUPAC, the International Union for Pure and Applied Chemistry, was established in 1919 to set these naming rules. The naming process for alkanes depends on the length of the carbon chain, the number of substituents, and where those substituents are placed. The first step is to find...

physical properties of alkanes

How Alkane Chain Length Changes Properties

Alkane properties change with chain length and molecular shape. Alkanes contain only carbon and hydrogen, so they are nonpolar molecules. The electronegativity difference between carbon and hydrogen is very small, and alkanes therefore have a zero dipole moment. As a result, the only forces between alkane molecules are dispersion forces. Dispersion forces depend on surface area. In straight-chain alkanes, surface area increases as the carbon chain gets longer. That means dispersion forces also...

newman projections

Molecule Rotations in Newman Projections

Newman projections show molecule rotations around a single bond in a clear two-dimensional view. Chemists use several notations to show the three-dimensional shape of a molecule on a flat surface. The dash-wedge formula is one common way to do this. In that notation, dashed wedges show groups behind the plane, solid wedges show groups coming out of the plane, and plain lines show groups in the plane. Organic molecules can rotate around single bonds. This rotation creates many temporary...

conformations of ethane and propane

Ethane Rotation: Staggered vs Eclipsed

Ethane and propane show how rotation around a carbon-carbon single bond changes a molecule’s shape and energy. This internal rotation creates conformers, which are different arrangements of the same molecule. For ethane, the main conformations are staggered and eclipsed. Staggered ethane is the lower-energy, more stable form. In this shape, the C-H bonds on the front carbon sit 60° away from the C-H bonds on the back carbon. This spacing reduces torsional strain, which is the repulsion that...

conformations of butane

Butane’s Anti, Gauche, and Eclipsed Forms

Butane has several conformations, or shapes made by rotation around a carbon-carbon bond. Unlike ethane and propane, which have only two major conformations, butane shows more than two conformers. The lowest-energy form is the staggered anti conformer. In this shape, the two bulky methyl groups sit opposite each other at a dihedral angle of 180°. This spacing reduces steric repulsion, so the anti form is the most stable. Butane also has two other staggered conformations. These are degenerate,...

cycloalkanes

Cycloalkane Rings and Naming Rules

Cycloalkanes are saturated hydrocarbons with carbon atoms arranged in rings. Because they have two fewer hydrogen atoms than the matching open-chain alkane, their general formula is CnH2n. These ring structures are a common topic in organic chemistry. Chemists often draw cycloalkanes with line-angle formulas. In this shortcut, regular polygons stand for the ring, and each side shows a carbon-carbon bond. The number of corners in the polygon matches the number of carbons in the ring. Naming...

conformations of cycloalkanes

Cycloalkane Ring Strain and Shapes

Cycloalkane ring strain depends on ring shape, bond angles, and bond rotation. Adolf von Baeyer first tried to explain the stability of cycloalkanes with angle strain, which is the strain caused when bond angles differ from the ideal 109.5° tetrahedral angle for sp3-hybridized carbons. His idea worked well for some small rings, but not for every cycloalkane. Cyclopropane and cyclobutane are strained, as expected from their compressed bond angles. Cyclopentane is more strained than Baeyer...

conformations of cyclohexane

Cyclohexane Chair, Boat, and Twist-Boat Forms

Cyclohexane adopts non-planar shapes because a flat ring would create high angle strain and torsional strain. The molecule instead bends into chair and boat conformations. These shapes lower the strain and make the ring more stable. The chair conformation is the most stable form. It is named for its easy-chair shape. In this form, two carbon atoms sit out of the plane, with one above and one below. This arrangement minimizes torsional strain. The bond angles are also very close to the ideal...

chair conformation of cyclohexane

Cyclohexane Ring Flip and Axial Bonds

Cyclohexane is most stable in the chair conformation. In this shape, the ring avoids angle strain because its bond angles are close to the ideal tetrahedral angle of 109.5°. It also avoids torsional strain because the bonds are arranged in a perfectly staggered way. In the chair form, the hydrogen atoms attached to cyclohexane carbons take two positions: axial and equatorial. Axial bonds point straight up or down and run parallel to the ring axis. Equatorial bonds point outward, roughly along...

stability of substituted cyclohexanes

Cyclohexane Chair Axial vs Equatorial

Cyclohexane chair conformations are shaped by the position of a substituent, and that position can change how stable the molecule is. The two chair forms of cyclohexane interconvert rapidly at room temperature. For unsubstituted cyclohexane, both chairs have the same energy and the same stability, so each appears in equal amount at equilibrium. When a hydrogen atom is replaced by a functional group, the two chair forms are no longer equal. In methylcyclohexane, the CH3 group is axial in one...

disubstituted cyclohexanes: cis-trans isomerism

disubstituted-cyclohexanes-cis-trans-isomerism

Cyclohexane Chair Stability and Bulky Groups

Disubstituted cyclohexanes can differ in both cis-trans arrangement and chair stability. In a cyclohexane ring, the substituents may sit on the same side of the ring or on opposite sides. These cis and trans stereoisomers have different physical properties, and they cannot switch into each other without breaking carbon-carbon bonds. Cyclohexane also has chair conformers, which place substituents in axial or equatorial positions. For 1,4-dimethylcyclohexane, the cis isomer has two conformers...

combustion energy: a measure of stability in alkanes and cycloalkanes

combustion-energy-a-measure-of-stability-in-alkanes-and-cycloalkanes

Why Branched Alkanes Burn More Cleanly

Alkanes are low-reactivity hydrocarbons because their C–C and C–H sigma bonds are non-polar. That is why they were once called paraffins, from the Latin words parum, meaning “too little,” and affinis, meaning “affinity.” In the presence of excess oxygen and high heat, alkanes undergo combustion to form carbon dioxide and water. Combustion is the energy source for natural gas, liquified petroleum gas (LPG), fuel oil, gasoline, diesel fuel, and aviation fuel. The heat released in this reaction,...

key terms and concepts

Learn how IUPAC names alkanes by finding the parent chain, adding substituents, and numbering carbons for the lowest possible locant.

Naming Alkane Chains and Substituents | JoVE K12

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Naming Alkane Chains and Substituents

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