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Hydrocarbon Chain

As the name suggest, the molecules of hydrocarbon consist of carbon and hydrogen as the main components and follow the catenation property of carbon to make huge chain of these compounds. Depending upon the composition of carbon and hydrogen combination, these are further categorized mainly as alkanes, alkenes and alkynes along with cycloalkanes and arenes.

A hydrocarbon chain component is substituted by a principle group at one of the terminals and attached by a single bond to an arbitrary ring component at the other terminus. The principal group must be expressed with a suffix and not as a functional group. These and more such important facts about hydrocarbon chain can be learnt as we combine the rules of organic reactions and component structures.


Hydrocarbon Chain Definition

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For any hydrocarbon chain component the position of the next component or part of the chain depends upon the molecular skeleton parent. The hydrocarbon chain component extends only from the principle group to the ring component or the substituted functional component. 

While naming the hydrocarbon chain the parent name of the hydrocarbon precedes the unchanged name of the hydrocarbon chain component and hence the suffix is appended as the hydrocarbon chain component with principle group occurs repeatedly and prefix with either di, tri or tetra to signify the number of times the component repeats.

Hydrocarbon Chain Names

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A molecular skeleton parent is an unbranched acyclic or cyclic molecular skeleton or an ensemble of such skeletons in the case of conjunctive names which remains after removal of all characteristic groups and or substitutes and also their substitution by H atoms and moreover, the seniority for the choice of the parent name according to the hierarchy criteria.

A parent substituent is generally derived from a molecular skeleton parent, or if it is a molecular skeleton parent with free valence and has seniority for the choice of the parent substituent name according to the hierarchy criteria.

A functional parent is a structure with substitutable H atoms whose name denotes a characteristic group. It’s a choice determined by the choice of senior compound class as per the criteria.

A stereo parent is an acyclic or cyclic senior structure with a semi trivial name or specialist name which may characteristic group or substituents. A stereo parent is senior to a corresponding name of a substituted molecular skeleton parent built with suitable prefixes and suffixes.

For the determination of the molecular skeleton parent, the following rules are applied in turn until a choice occurs.
  • Senior is the choice chain or ring structure which bears the largest number of principal group
  • For structures to which conjunctive nomenclature can be applied, the hydrocarbon chain component together are considered to be the molecular skeleton parent as a whole.
  • Senior is the chain structure with senior hetero atom content in agreement with seniority order of the compound class. The molecular skeleton parent contains with decreasing seniority one or several atoms of the following order.
N > P > As > Sb > Bi > B > Si > Ge > Sn > Pb > O > S Se > Te 
  • If a structure contains a chain and ring partial structure of the same compound class concerning the hetero atom content or that the number of the senior hetero atoms in the ring or chain partial structure does not play any role.
  • For a structures to which conjunctive nomenclature must be applied the skeleton consisting of the hydrocarbon chain component is regarded as the main structure.
  • For structures to which conjunctive nomenclature must be applied needs to be consulted if the principal group occurs in the same number both in hydrocarbon chain component as well as ring component
The names of alcohols, aldehydes, ketones and various acids are based on the name of the hydrocarbon with an appropriate suffix to denote the class of compounds as follows:
  • The alcohols are substituted with ‘ol’ for the final ‘e’ in the name of hydrocarbon and also designate the position of –OH group by the number of the carbon atom. The names of the hydrocarbon is based on the –OH group attached to the carbon atoms and hence gets specific number.
  • Example: $CH_{3}CH_{2}CHOHCH_{3}$ is derivative of 4 carbon hydrocarbon butane and is termed as 2 butanol
  • The aldehydes are substituted with ‘al’ for the final ‘e’ in the name of hydrocarbon. By definition the carbon atom of aldehyde is carbon – 1 in the hydrocarbon chain. Example: $CH_{3}CH(CH_{3})CH_{2}CH_{2}CHO$ has 5 carbon chain with the aldehyde functional group being carbon -1 and $–CH_{3}$ group at position 4 and hence the name of 4 methyl pentanal.
  • The ketones are substituted ‘one’ for the final ‘e’ in the name of hydrocarbon and the position of ketone functional group or carbonyl group is indicated by the number of carbon atom. For example, the 4-ethyl 2-hexanone is having position 2 carbonyl group and position 4 ethyl group for a 6 member chain hydrocarbon. $CH_{3}COCH_{2}CH(C_{2}H_{5})CH_{2}CH_{3}$
  • The carboxylic acids or organic acids are substituted with ‘oic’ for the final ‘e’ in the name of hydrocarbon. The carbon atoms in the longest chain are counted beginning with carboxylic carbon atom.

Hydrocarbon Chain Examples

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There are several hydrocarbon chain examples and each of these follow a certain set of specific rules which are applied for each one of these.

Alkane series:
Methane $CH_{4}$, Ethane $C_{2}H_{6}$, Propane $C_{3}H_{8}$, Butane $C_{4}H_{10}$ and Pentane $C_{5}H_{12}$ etc.

Alkene series:
Ethene $C_{2}H_{4}$, Propene $C_{3}H_{6}$, Butene $C_{4}H_{8}$ and Pentene $C_{5}H_{10}$ etc.

Alkyne series:
Ethyne $C_{2}H_{2}$, Propyne $C_{3}H_{4}$, Butyne $C_{4}H_{6}$ and Pentyne $C_{5}H_{8}$ etc.

Alcohol series (-OH):
Methanol $CH_{3}OH$, Ethanol $C_{2}H_{5}OH$, Propanol $C_{3}H_{7}OH$, Butanol $C_{4}H_{9}OH$ and Pentanol $C_{5}H_{11}OH$ etc.

Aldehyde series (-CHO):
Methanal HCHO, Ethanal $CH_{3}CHO$, Propanal $C_{2}H_{5}CHO$, Butanal $C_{3}H_{7}CHO$ and Pentanal $C_{4}H_{9}CHO$ etc.

Ketone series (-CO):
Methanone, Ethanone, Propanone, Butanone, Pentanone and Hexanone etc.

Carboxylic acid (-COOH):
Methanoic acid, Ethanoic acid, Propanoic acid, Butanoic acid, Pentanoic acid, and Hexanoic acid etc.

Chemical Formula of Hydrocarbon

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Most of the chemical formula of hydrocarbon follow a specific set of rules and gives a generic formula to identify the homologous series and chemical characteristics. The generic formula shows C as carbon atom, H as hydrogen atom and n as integer.

Alkane series:

Alkene series:

Alkyne series:

Alcohol series:
$C_{n}H_{2n}+1 – (OH)$

Aldehyde series:
$C_{n}H_{2n}+1 – (CHO)$

Ketone series:
$C_{n}H_{2n}+1 – (CO)$

Carboxylic acid series:
$C_{n}H_{2n}+1 – (COOH) $

How to Crack a Long Chain Hydrocarbon?

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When organic raw compounds are heated enough they tend to break up and is better known as thermal decomposition. The long chain hydrocarbons can be broken into smaller and more useful smaller molecules by the same thermal decomposition. This chopping up of bigger organic molecules into smaller more useful by using heat is called cracking.

The cracking process is built into the oil refinery when the unwanted long chain hydrocarbons are heated by pre-boiled water drum or chambers. The vapour is passed over a hot catalyst and thereby the thermal decomposition takes place making new smaller more useful hydrocarbons.
The utility of catalysts is just to speed up the reaction and a catalyst used during cracking helps in making the thermal decomposition reaction go faster.

The short chain products are passed back through fractionating tower to separate these molecules out.

The extra amount of petrol needed is produced in this manner and also to make plastic utility products.

Crude oil – (furnace) $\rightarrow$ [ fractionating tower] $\rightarrow$ useful products

Fractionating tower – [excess long chain fractions] $\rightarrow$ (cracker) 

Cracker $\rightarrow$ [cracked products are re-distilled] $\rightarrow$ furnace.
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