Heptane
Overview
 
n-Heptane is the straight-chain alkane
Alkane
Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...

 with the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 H3C(CH2)5CH3 or C7H16. When used as a test fuel component in anti-knock test engines, a 100% heptane fuel is the zero point of the octane rating
Octane rating
Octane rating or octane number is a standard measure of the anti-knock properties of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating...

 scale (the 100 point is a 100% iso-octane
2,2,4-Trimethylpentane
2,2,4-Trimethylpentane, also known as isooctane, iso-octane, is an organic compound with the formula 3CCH2CH2. It is one of several isomers of octane . This particular isomer is the standard for 100 point on the octane rating scale...

). Octane number equates to the anti-knock qualities of a comparison mixture of heptane and isooctane which is expressed as the percentage of isooctane in heptane and is listed on pumps for gasoline dispensed in the United States and internationally.
Heptane (and its many isomers) is widely applied in laboratories as a totally non-polar solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

.
Encyclopedia
n-Heptane is the straight-chain alkane
Alkane
Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...

 with the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 H3C(CH2)5CH3 or C7H16. When used as a test fuel component in anti-knock test engines, a 100% heptane fuel is the zero point of the octane rating
Octane rating
Octane rating or octane number is a standard measure of the anti-knock properties of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating...

 scale (the 100 point is a 100% iso-octane
2,2,4-Trimethylpentane
2,2,4-Trimethylpentane, also known as isooctane, iso-octane, is an organic compound with the formula 3CCH2CH2. It is one of several isomers of octane . This particular isomer is the standard for 100 point on the octane rating scale...

). Octane number equates to the anti-knock qualities of a comparison mixture of heptane and isooctane which is expressed as the percentage of isooctane in heptane and is listed on pumps for gasoline dispensed in the United States and internationally.

Uses

Heptane (and its many isomers) is widely applied in laboratories as a totally non-polar solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

. As a liquid, it is ideal for transport and storage. In the grease spot test, heptane is used to dissolve the oil spot to show the previous presence of organic compounds on a stained paper. This is done by shaking the stained paper in a heptane solution for about half a minute.

Aqueous bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

 may be distinguished from aqueous iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....

 by its appearance after extraction
Extraction (chemistry)
Extraction in chemistry is a separation process consisting in the separation of a substance from a matrix. It may refer to Liquid-liquid extraction, and Solid phase extraction....

 into heptane. In water, both bromine and iodine appear brown
Brown
Brown is a color term, denoting a range of composite colors produced by a mixture of orange, red, rose, or yellow with black or gray. The term is from Old English brún, in origin for any dusky or dark shade of color....

. However, iodine turns purple
Purple
Purple is a range of hues of color occurring between red and blue, and is classified as a secondary color as the colors are required to create the shade....

 when dissolved in heptane, whereas the bromine solution remains brown.

Heptane is commercially available as mixed isomers for use in paints and coatings, as the rubber cement
Rubber cement
Rubber cement is an adhesive made from elastic polymers mixed in a solvent such as acetone, hexane, heptane or toluene to keep them fluid enough to be used. Water-based formulas, often stabilised by ammonia, are also available...

 solvent "Bestine", the outdoor stove fuel "Powerfuel" by Primus, as pure n-Heptane for research and development and pharmaceutical manufacturing and as a minor component of gasoline.

Octane rating scale

n-Heptane is the zero point of the octane rating
Octane rating
Octane rating or octane number is a standard measure of the anti-knock properties of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating...

 scale. It is undesirable in petrol, because it burns explosively, causing engine
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...

 knocking
Engine knocking
Knocking in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.The...

, as opposed to branched-chain octane
Octane
Octane is a hydrocarbon and an alkane with the chemical formula C8H18, and the condensed structural formula CH36CH3. Octane has many structural isomers that differ by the amount and location of branching in the carbon chain...

 isomers, which burn more slowly and give better performance. It was chosen as the zero point of the scale because of the availability of very high purity n-heptane, unmixed with other isomers of heptane or other alkanes, distilled from the resin
Resin
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...

 of Jeffrey Pine
Jeffrey Pine
The Jeffrey Pine, Pinus jeffreyi, named in honor of its botanist documenter John Jeffrey, is a North American pine related to Ponderosa Pine.-Distribution and habitat:...

 and from the fruit of Pittosporum resiniferum
Pittosporum resiniferum
The petroleum nut, Pittosporum resiniferum, is a tree that grows in the Philippines, particularly in the wilderness surrounding the Mayon Volcano. The petroleum nut derives its name from the resemblance of the fruit's odor to petroleum-based fuels. The fruits of the tree burn brightly when...

. Other sources of heptane and octane, produced from crude oil, contain a mixture of different isomers with greatly differing ratings and do not give as precise a zero point. ChevronPhillips Specialty Chemical produces a specialized grade of high purity n-Heptane (>99.0%) from crude oil through precision refining and distillation that is used in the measurement of octane rating for fuels.

Isomers and enantiomers

Heptane has nine isomer
Isomer
In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...

s, or eleven if enantiomer
Enantiomer
In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are non-superposable , much as one's left and right hands are the same except for opposite orientation. It can be clearly understood if you try to place your hands one over the other without...

s are counted:
  • Heptane (n-heptane), H3C–CH2–CH2–CH2–CH2–CH2–CH3,
  • 2-Methylhexane
    2-Methylhexane
    2-Methylhexane is an isomer of heptane. It is structurally a hexane molecule with a methyl group attached to its second carbon atom...

     (isoheptane), H3C–CH(CH3)–CH2–CH2–CH2–CH3,
  • 3-Methylhexane
    3-Methylhexane
    3-Methylhexane is a branched hydrocarbon. It is one of the isomers of heptane....

    , H3C–CH2–C*H(CH3)–CH2–CH2–CH3 (chiral
    Chirality (chemistry)
    A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....

    ),
  • 2,2-Dimethylpentane (neoheptane), (H3C)3–C–CH2–CH2–CH3,
  • 2,3-Dimethylpentane, (H3C)2–CH–C*H(CH3)–CH2–CH3 (chiral),
  • 2,4-Dimethylpentane, (H3C)2–CH–CH2–CH–(CH3)2,
  • 3,3-Dimethylpentane, H3C–CH2–C(CH3)2–CH2–CH3,
  • 3-Ethylpentane
    3-Ethylpentane
    3-Ethylpentane is a branched, saturated hydrocarbon. It is an alkane, and one of the many structural isomers of heptane, consisting of a five carbon chain with a two carbon branch at the middle carbon....

    , H3C–CH2–CH(CH2CH3)–CH2–CH3,
  • 2,2,3-Trimethylbutane, CH3–C(CH3)2–CH(CH3)–CH3, this isomer is also known as pentamethylethane and triptane.

External links

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