The Characterization of Hydrocarbons

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BioOrganic Chemistry Laboratory – CH 205 (2015-2016) Experiment 5

The Characterization of Hydrocarbons

Charisse Mulles, Jeremy Paatan, Paolo Perez, Rayesha Azzedine Ma. G. Quilala*

Department of Sports Science, College of Rehabilitation Sciences

University of Santo Tomas, España Street, Manila 1008

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Abstract:

In the experiment, the characteristics of hydrocarbons are known through Nitration test, Bromine test and Permanganate test. Wherein the test compounds, which are the used hydrocarbons in the experiment, namely cyclohexane, cyclohexene, toluene and naphthalene are

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Introduction

           Hydrocarbon molecule compose of only carbon (C) and hydrogen (H). The carbon atoms join together to form the framework of the compound; the hydrogen atom attach to them in many different configuration. It is possible for double or triple bonds to form between carbon atoms and even for structure, such as rings. Hydrocarbons can be grouped into two classes: aliphatic hydrocarbons and aromatic hydrocarbons.

           Aliphatic hydrocarbons are non-aromatic compounds. They do not contain benzene ring in the structure. Saturated hydrocarbons and unsaturated hydrocarbons are the examples of an aliphatic hydrocarbons. Saturated hydrocarbons, or commonly called as alkanes, contain only carbon and hydrogen and have no multiple bonds between carbon atoms. Alkanes have molecular formulas CnH2n + 2  (where n is an integer). Alkanes can be classified as cycloalkanes. Cycloalkanes are type of alkane having C-C single bond in a ring structure. There is not much electronegativity difference between carbon and hydrogen, so there is hardly any bond polarity. The molecules themselves also have very little polarity. A totally symmetrical alkane molecule is completely non-polar. This means that the only attractions between one molecule and its neighbors will be Van der Waals dispersion forces. These will be very small for a low number carbon alkane, but will increase as the molecules get bigger. That’s why the boiling points of the alkanes increase with molecular size.

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           Unsaturated hydrocarbons have at least one C-C double and/or triple bond. Alkene is an unsaturated hydrocarbon with a carbon-carbon double bond, and Alkyne is also an unsaturated hydrocarbon with a carbon-carbon triple bond. The alkene has a boiling point which is a small number of degrees lower than the corresponding alkane. The only attractions involved are Van der Waals dispersion forces, and these depend on the shape of the molecule and the number of electrons it contains. Each alkene has two fewer electrons than the alkane with the same number of carbons. In alkyne, the importance of a triple bond is valued. It allows the uniqueness of its structure. This triple bond contributes to the nonpolar bonding strength, linear, and the acidity of alkynes. 

             On the other hand, Aromatic hydrocarbons are those which contain one or more benzene ring. It has a pattern of bonding that makes it chemically stable.

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Methodology

            The first test performed was the nitration test. 10 drops of colorless test compounds (cyclohexane, cyclohexene, toluene and naphthalene) were placed in separate test tubes. 10 drops nitrating reagent (H2SO4/HNO3) was added to each of the test compounds in the test tubes, and the test tubes were shaken. In this process, only cyclohexene, toluene and naphthalene changed its color of solution, and cyclohexane remained colorless.  After shaking, the test compounds with the added nitrating reagent were warmed in the water bath for 1 minute. After a minute in the water bath, the test compounds were cooled, and added 20 drops of distilled water. There were two layers produced by the nitration test in cyclohexene, toluene and naphthalene: the upper or organic layer and the lower layer. It means that only cyclohexene, toluene and naphthalene reacted with the nitrating reagent.

         In bromine test, 10 drops of colorless test compounds were also placed in separate test tubes. A bromine reagent (bromine in DCM, an orange solution) was added dropwise in each test compounds and was shaken occasionally until no color change occurred. Cyclohexane and toluene, two colorless liquid changed its color into an orange by adding just 1 drop of the bromine reagent. Naphthalene, also a colorless liquid change into red-orange color liquid when added with 1 drop of the reagent. The 20 drops of bromine reagent disappeared in cyclohexene.

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