There are a few widespread misconceptions about this topic. The original question, edits, and comments give the impression that such misconceptions may also contribue to the confusion in this case. Therefore, we should like to clear up some of the misconceptions first.
High-octane fuel does not contain a high concentration of octane.
The composition of gasoline varies widely; anyway, typical gasoline contains less than 1 % octane.
The octane number of gasoline does not describe the composition of gasoline. It refers to the measurement of the knock resistance of gasoline, which is usually expressed by their research octane number (RON) or motor octane number (MON). Both parameters are determined in single-cylinder four-stroke test engines with an adjustable compression ratio according to standardized test procedures, e.g. EN 25164 or ASTM D 2699 for RON, and EN 25163 or ASTM D 2700 for MON. During the measurement, the compression ratio is raised until a certain standardized level of knocking is reached. The corresponding octane number is determined by finding a reference mixture of heptane and “octane” that gives the same knock level. The octane number is the fraction of “octane” (in %) in the “octane”-heptane mixture. For example, gasoline with an octane number of 95 has the same knocking performance as a mixture of 95 % “octane” and 5 % heptane; however, this does not mean that the gasoline contains 95 % “octane”.
Nevertheless, the wrong idea that gasoline would contain a high concentration of octane is widespread. For example, in the first relevant Google hit, Ritter, S. Chem. Eng. News 2005, 83 (8), 37:
Octanes are an important component of gasoline because they help provide smoother combustion in the car’s cylinders and prevent knocking.
Also remarkable is the fact that many textbooks and lectures select the combustion reaction of octane of all the possible combustion reactions of gasoline to show the principle of combustion:
$$\ce{2C8H18 + 25 O2 -> 16 CO2 + 18 H2O}$$
The reference substance for the octane number is not octane.
The octane number refers to a mixture of heptane and “octane”. However, the “octane” used for this mixture is not the unbranched alkane octane. It is actually a branched isomer of octane with the traditional name “isooctane”. Thus, gasoline with an octane number of 95 actually has the same knocking performance as a mixture of 95 % “isooctane” and 5 % heptane; however, this also does not mean that the gasoline contains 95 % “isooctane”.
The octane number of pure octane is actually very low. Its knock resistance is worse than the performance of pure heptane, which has a octane number of zero by definition.
The “isooctane” that is used as a reference substance for the octane number is not isooctane.
The name isooctane was in accordance with older nomenclature rules. The corresponding systematic name according to current IUPAC recommendations is 2-methylheptane. However, the “isooctane” that is used for the determination of the octane number is not isooctane, i.e. it is not 2-methylheptane. This “isooctane” actually is 2,2,4-trimethylpentane, which is another isomer of octane. Thus, gasoline with an octane number of 95 actually has the same knocking performance as a mixture of 95 % 2,2,4-trimethylpentane and 5 % heptane; and once again, this does not mean that the gasoline contains 95 % 2,2,4-trimethylpentane.
By way of comparison, the octane number of pure isooctane (2-methylheptane) is only about 23.
Irrespective of which compound is really meant in the original question (octane, 2-methylheptane, or 2,2,4-trimethylpentane; the question and comments also mention the similar alkenes 6-methylhept-1-ene and 2,4,4-trimethylpent-1-ene, which might be a mistake), such components of gasoline are usually not selectively synthesized in a pure form.
Gasoline consists of hundreds of different compounds, and the exact composition can vary widely. It is produced by blending of different product streams of oil refining. Today, only a small part (so-called straight-run gasoline) is directly obtained by distillation of crude oil. Other important product streams are thermally cracked gasoline, catalytically cracked gasoline, catalytic reformate (so-called platformate), isomerate, alkylate, polymer gasoline, and oxygenates.
