How Many Isomers of Heptane

Introduction

There are different types of isomers of heptane including stereoisomers, diastereomers, enantiomers and structural isomers. Organic chemistry was in its infancy during the first part of the 19th century. Bonds as we now understand them were unknown. Compound structures were unknown, and some people at the time believed there was no way to learn anything about structure if there ever existed any. At the time, chemists were honing their ability to use gravimetric and combustion analyses to ascertain the composition of substances. The physical characteristics of two distinct alkanes, such as their melting point, boiling point, refractive index, etc., were always different if it was discovered that their carbon and hydrogen contents varied. They were distinct, in fact. In multiple cases, compounds with diverse physical properties were found to have exactly the same elemental composition and molecular weight.

Constitutional (Structural) Isomers

The only difference between constitutional isomers is in how connected their atoms are. The number of constitutional isomers that can exist for each of the acyclic alkanes CnH2n+2 is shown in the chart below, where n = (1 to 10). The range of constitutional isomers rapidly expands as the number of carbon atoms does.

Stereoisomers

The sole difference between stereoisomers and other isomers is how the atoms are oriented in space. Geometrical isomers, diastereomers, and enantiomers are examples of stereoisomers. Enantiomers are the first concept in the most typical formulation of these three types. Enantiomers are stereoisomers that cannot be superimposable or reversed. Stereoisomers that do not mirror images of one another are referred to as stereoisomers. Stereoisomers centred on a double bond are geometric isomers (cis-trans). Rather than discuss the more complex stereoisomers first — for indeed we have been progressing from the more complex isomers to the less complex ones — we will consider enantiomers in the next section first, and then work our way toward the other stereoisomers — diastereomers and geometrical isomers.

1. Enantiomers

Simply put, enantiomers are a pair of stereoisomers that cannot be superimposed upon one another. To be an enantiomer, a substance must be chiral (handed), that is, devoid of planes of symmetry or centres of symmetry. Only in pairs, enantiomers cannot be superimposed over one another. The most typical chiral entity is a hand. Your right hand and left hand are mirror images of one another and cannot be superimposed. The majority of knots, spiral staircases, gloves, shoes, fasteners, and other everyday items are chiral. An item must have at least one plane of symmetry in order to be considered achiral. Examples include, to a first approximation, the external body of a human being (bilateral symmetry), a coffee cup, a pair of reading glasses, etc.

The most frequent formation of enantiomers involves a carbon atom with four distinct substituents (sp3 hybridised). Quadrivalent carbon can be modified in two different ways. The two configurations are one another's enantiomers. It is a common misconception that the carbon atom in these species is chiral. The environment in which the carbon atom exists determines whether it is chiral or not.

2. Diastereomers

Stereoisomers that are not enantiomers are called diastereomers. How is that even possible? Consider two red, yellow, and green atoms that are attached to two grey tetrahedral "asymmetric carbons" that are bound to one another.

3. Geometrical Isomers

Stereoisomers about double bonds are geometric isomers, often known as E/Z isomers. They are achiral. Both isomers of (E)-2-butene (left below) and (Z)-2-butene (right below) are achiral compounds that can be superimposed on one another. They are not (easily) interconvertible since they are all distinct alkenes with different characteristics. The strong double bond (grey atoms) cannot be rotated around.

Conclusion

Nine different chain isomers of heptne exist, including n-heptane, 2-methylhexane, 3-methylhexane, 2,3,4, 2,2,2,2,2-dimethylpentane, 3,3,3,3-dimethylpentane, 3-ethylpentane, and 2,2,3,3-trimethylbutane.