Branched-Chain Alkanes

The structure of butane (C4H10) can be written down by stringing four carbon atoms together in a row. Although the compound butane has this structure, there is another way to combine four carbon atoms and ten hydrogen atoms to form a molecule. Assemble three carbon atoms in a row, and then branch the fourth carbon atom off the middle carbon atom: Next, we’ll add enough hydrogen atoms to give each carbon atom four bonds, which will complete the structure.

Branched chain alkanes

The structure of isobutane consists of a continuous chain of three carbon atoms only, with the fourth carbon atom attached as a branch off the middle carbon atom of the continuous chain, in contrast to the structures of butane and ethane, which consist of two continuous chains of carbon atoms.

Instead of being isomeric with C4H10, the compounds methane (CH4), ethane (C2H6), and propane (C3H8) are not isomeric with C4H10 because there is only one way to arrange the atoms in each formula so that each carbon atom has four bonds.

Butane and isobutane are two types of butane. The ball-and-stick models of these two compounds reveal that they are isomers; both have the molecular formula C4H10, which indicates that they are related.

The chemical symbol C4H10 is represented by a twisted chain. It is possible to bend the four-carbon chain in a variety of ways because the groups can freely rotate around the C–C bonds. However, the identity of the compound is not altered as a result of this rotation. We must remember that bending the chain does not change the identity of any compound.

Pentane is the next homologous compound after C4H10 in the homologous series. In terms of molecular formula, each compound has the same value: C5H12. This is due to the fact that it contains all five carbon atoms in a single continuous chain at the far left of the compound. In the middle of the chain, there is isopentane, which, like isobutane, has a CH3 branch off the second carbon atom of the continuous chain, but only has one CH3 branch.

Neopentane (from the Greek neos, which means “new”) was given to the compound on the far right because it was discovered after the other two. Despite the fact that all three have the same molecular formula, they have distinct properties, including boiling points that are 36.1°C for pentane, 27.7°C for isopentane, and 9.5°C for neopentane.

Despite the fact that the tetrahedral arrangement around each carbon atom gives it a zigzag shape, a continuous (unbranched) chain of carbon atoms is commonly referred to as a straight chain. Straight-chain alkanes are sometimes referred to as normal alkanes, and their names are preceded by the prefix n- to distinguish them from other alkanes. For instance, butane is referred to as n-butane.

Effect of branching

So here are the interrelationships to consider:

Compared to branched structures, linear structures have higher melting and boiling points due to better stacking and surface area contact.

high branching vs. low branching –> more sphere-like –> better stacking –> higher melting point.

Highly branched vs. unbranched —>more sphere-like –-> lower surface area –-> lower boiling point.

If all of this appears to be ambiguous, contradictory, and imprecise, you are correct in your assessment. It is not a simple subject to discuss. As a final example, I’ll give you 2,2,3,3,3-tetramethylbutane, which stands for 2,2,3,3,3-tetramethylbutane. Isooctane (gasoline) is an isomer of isooctane with a melting point of 95 degrees Celsius. 

Formula for alkane

Alkanes have the general formula of CnH2n+2 where n is the number of carbon atoms. 

Conclusion

Branched hydrocarbons are named using the names of their substituents combined with the hydrocarbon’s parent name, without the use of spaces between the names. There is, however, most likely one more step to take. The hydrocarbon’s longest chain must be numbered, and the locant (numerical position of the substituent) must be included in order to account for the possibility of isomers occurring. In the same way that double and triple bonds are numbered, the main chain is numbered in order to give the substituent the smallest number possible.