[Chemistry Class Notes] on Alcohol Hydroxyl Group Pdf for Exam

Introduction

Organic chemistry has always been a wider research subject among science enthusiasts. The basic organic chemistry’s idea is to propagate the elementary information about the organic compounds, exist around us and provide a solid foundation concerning the further exploration of organic compounds and factors that govern the properties of these compounds.

The organic compounds form a series, called homologs series, where the successive compounds contain similar functional groups and vary from one another by a –CH2 group. Alcohol is one of the various functional groups that are found in organic compounds. Let us discuss more on the structure of alcohol, phenol, and others.

What is Alcohol?

Alcohols are organic compounds, where an aliphatic carbon or a hydrogen atom is replaced with the hydroxyl group. Therefore, an alcohol molecule consists of two parts; one containing the alkyl group and another containing the hydroxyl group, and they have a sweet odor. They exhibit a unique set of both physical properties and chemical properties. The both physical and chemical properties of alcohol are primarily due to the hydroxyl group presence. The alcohol structure depends on different factors.

Alcohols are classified into various groups based on where the hydroxyl group is placed in the molecule. This results in a few differences in the chemical properties. The classification of alcohol is given as follows:

Primary Alcohols

In primary alcohol, the carbon with the hydroxyl group will only be attached to a single or one alkyl group.

Some examples of primary alcohols are given below in the diagrammatic representation.

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Methanol is an exception to the above representation. Still, it is the primary alcohol though the carbon, having the hydroxyl group attached does not have any other alkyl group attached to it.

Secondary Alcohols

In secondary alcohol, the carbon with the hydroxyl group will be attached to the two alkyl groups.

Some examples of secondary alcohols are represented below:

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Tertiary Alcohols

The carbon present with the hydroxyl group gets attached to three other alkyl groups in the tertiary alcohol.

Some examples of tertiary alcohols are depicted below.

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Alcohol Structure

The alcohol atomic structure is primarily attributed to the presence of the hydroxyl group alcohol. In alcohols, the main chain’s carbon atom gets bonded to the oxygen atom of the hydroxyl group alcohol by a sigma (σ) bond.

This sigma bond is formed because of the overlap of an sp3 hybridized orbital of carbon with an oxygen atom’s sp3 hybridized orbital. Because of the repulsion between the unshared electron oxygen pairs, the bond angle of the C-O-H bonds present in alcohol is slightly less than that of the tetrahedral angle (109°-28′).

The structure of Alcohol can be represented as follows:

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Structure of Phenol

Phenol structure is primarily attributed to two main factors, as listed below:

• The partial double bond character because of the resonance occurs in the aromatic ring due to a conjugated electron pair of oxygen.

• Hybridization is the carbon to which the oxygen atom of the hydroxyl group is. The carbon atom attached to the oxygen is sp2 hybridized in phenol.

Hence, the C-O bond length in phenol is slightly less than that of methanol.

The structure of phenol can be represented as below:

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Ether Structure

• An ether molecule contains a tetrahedral structure.

• Because of the repulsive interaction between the two bulky (–R) groups, the bond angle (R-O-R) is a bit greater than the tetrahedral angle.

• The C–O bond length present in ether is almost similar to that as in alcohol.

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Nomenclature of Alcohol

Etymology

The term “alcohol” is introduced from an Arabic word, Arabic kohl, which is a powder used as an eyeliner. Al- is the definite article of Arabic that is equivalent to the in English. Alcohol was originally used for the fine powder, which is formed by the natural mineral stibnite sublimation to produce the antimony trisulfide Sb2S3.

It was also considered to be either as “spirit” or “essence” of this mineral. Moreover, it was used as an eyeliner, cosmetic, and antiseptic. Generally, the meaning of alcohol was extended to the distilled substances and then narrowed to ethanol, when a synonym, “spirits” was for hard liquor.

In the translation of John of Vigo, in 1543, Bartholomew Traheron introduces the word “barbarous” as a term used by authors for “fine powder.” He wrote, “the barbarous authors use alcohol, or (sometimes I find it as written) alcohol, for the finest powder.”

Lexicon Chymicum, in 1657, by William Johnson, glosses the word as “antimonium sive stibium.” By extension, the same word had come to refer to any fluid come by distillation, including “alcohol of wine,” the distilled essence of wine. Also, in 1594, Libavius in Alchymia referred to as, “vini alcohol vel vinum alcalisatum.”

Ethanol was invented in 1892 by combining the word ethane with “-ol” and ending up with “alcohol”.