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: R - OH

  1. #1

    Jul 2011

    R - OH

    What is an alcohol?
    "Alcohol" is a generic name for large group of organic chemical compounds. There are many types of alcohols. They all are derivatives of hydrocarbons in which one or more of the hydrogen atoms have been replace by a hydroxyl (-OH) functional group. Hydrocarbons are compounds with contain hydrogen (H) and carbon (C) only. The hydroxyl group imparts particular properties to the radical to which it is attached.
    Alcohols are named according to the radical to which the OH group is attached. For example if the OH group is attached to the methyl radical CH3 so that the compound is CH3OH, then one has methyl alcohol. If it is attached to the ethyl (C2H5) radical then one has ethyl alcohol (CH3CH2OH) - the alcohol we consume in beverages. The general formula for alcohol is ROH, where R signifies a hydrocarbon radical attached to an -OH group. A list of some of the common alcohols is given below:
    Alcohol Name Formula
    Methyl alcohol (methanol) CH3OH
    Ethyl alcohol (ethanol) CH3CH2OH
    n - propyl alcohol CH3CH2CH2OH
    Isopropyl alcohol (propanol -2) CH3CHOHCH3
    n-butyl alcohol (butanol -1) CH3(CH2)2CH2OH
    butyl alcohol (butanol -2) CH3CH2CHOHCH3
    n-hexyl alcohol (hexanol-1) CH3(CH2)4CH2OH
    n-heptyl alcohol (heptanol-1) CH3(CH2)5CH2OH
    n-octyl alcohol (octanol-1) CH3(CH2)6CH2OH
    ethylene glycol CH2OHCH2OH
    glycerol CH2OHCHOHCH2OH
    Alcohols are classified as primary, secondary, or tertiary dependent upon the number of other organic groups, denoted R, attached to the carbon atom with the hydroxyl ( OH) group. Those with two hydrogen atoms attached to the carbon atom with the attached hydroxyl group are called primary. Those with one hydrogen atom attached to the carbon with the hydroxyl group are called secondary, and those with no hydrogen atoms attached to the carbon atom with the hydroxyl group are called tertiary. Thus, a primary alcohol has the form RCH2 OH; a secondary alcohol has the form R2CH OH: and a tertiary alcohol, the form R3C OH. The R groups do not need to be the same.
    Ethyl Alcohol - for which the more scientific name is ethanol - is the substance that we find in beverages. For the remainder of this unit, consider the words ethyl alcohol, alcohol and ethanol to be interchangeable. An alternate representation of ethyl alcohol as a "ball and stick" molecular model appears below:
    There are other molecules that contain an -OH group - an oxygen bonded to a carbon. Water, H2O is the most common. It is not an alcohol because alcohols are defined as organic compounds that have little or no ionization of the hydrogen. Other organic compounds that contain -OH groups but are not alcohols are phenol (C6H5OH) and acetic acid (CH3COOH). These compounds are not alcohols because they are acidic. The term alcohol, then, is another representation of a type of electronic structure in the molecules of substances. Properties of Some Alcohols
    Boiling Point oC and Flammability and Toxicity-LD50
    (The dose, in mg/kg, that kills 50% of test animals, generally reported for rats.)
    bp flam LD50
    Methanol 65 yes 6500
    Ethanol 78 yes 7060
    Ethylene Glycol 198 no 4700
    Glycerol 290 no 12600

  2. #2

    Jul 2012

    : R - OH

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