Carbon compounds short note posted

Students always think that this topic is difficult. They worry that they can not memorise the chemical properties of alkane, alkene, alcohol and carboxylic acid.


In fact, chemical properties of carbon compound only contribute fewer mark. The most important part of this topic is the basic knowledge of carbon compounds.






(i) Definition


1.  Hydrocarbons are organic compounds that contain the elements carbon and hydrogen only.
2.  Saturated hydrocarbon is hydrocarbon that have only single covalent bonds between all the
     carbon atoms in the molecules.
3.  Unsaturated hydrocarbon is hydrocarbon that have at least one carbon-carbon multiple bond in
     the molecule.
4.  The molecular formula is a chemical formula that shows the actual numbers of atoms
     of each element present in one molecule of the substance.
5.  The structural formula of an organic compound is the chemical formula that shows the
     arrangement of atoms and covalent bonds between atoms in a molecule of the compound.
6. A homologous is a family of organic compounds with the same functional group and
     with similar chemical properties.
7. A functional group is an atom or a group of atoms that determines the characteristic properties
    of an organic compound.
8.  Isomerism is the existence of two or more compounds that have the same molecular formula but
     different structural formulae.
9.  Isomers are compounds which have the same molecular formula but different structural formulae.
     Each isomer has a different arrangement of atoms in space.


(ii) Naming carbon compounds


The increasingly large number of organic compounds identified with each passing day, together with the fact that many of these compounds are isomers of other compounds, requires that a systematic nomenclature system be developed. Just as each distinct compound has a unique molecular structure which can be designated by a structural formula, each compound must be given a characteristic and unique name.


The IUPAC nomenclature system is a set of logical rules devised and used by organic chemists to circumvent problems caused by arbitrary nomenclature. Knowing these rules and given a structural formula, one should be able to write a unique name for every distinct compound. Likewise, given a IUPAC name, one should be able to write a structural formula. In general, an IUPAC name will have three essential features:


• A root or base indicating a major chain or ring of carbon atoms found in the molecular structure.
• A suffix or other element(s) designating functional groups that may be present in the compound.
• Names of substituent groups, other than hydrogen, that complete the molecular structure.

Prefixes (root) for naming carbon chains

Suffix for naming functional group

Alkyl or Sunstituent group

Example

Word root: But (C₄)

Prefix       : 3, chloro

Suffix       : -ol

Name        :  3-chlorobutan-1-ol


http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry
http://www.acdlabs.com/iupac/nomenclature/
http://www.chemguide.co.uk/basicorg/conventions/names.html


(iii) Isomerism


Isomerism is the phenomenon whereby certain compounds, with the same molecular formula, exist in different forms owing to their different organisations of atoms. The concept of isomerism illustrates the fundamental importance of molecular structure and shape in organic chemistry.

http://www.chemguide.co.uk/basicorg/isomerism/structural.html
http://www.creative-chemistry.org.uk/molecules/hexane.htm (interactive)


(iv) Homologous series


In chemistry, a homologous series is a series of organic compounds with a similar general formula, possessing similar chemical properties due to the presence of the same functional group, and shows a gradation in physical properties as a result of increase in molecular size and mass.


CHARACTERISTICS OF A HOMOLOGOUS SERIES
1. STRUCTURAL FORMULA
    All the members of a homologous series have same structural formula.
2. MOLECULAR FORMULA
    Molecular formula of different members of a homologous series differs from previous and next member by CH₂.
3. NATURE OF ELEMENT
    All the members of series have same type of elements. 
4. FUNCTIONAL GROUP
    All the members of homologous series contain same functional group.
5. GENERAL FORMULA
    Members of a homologous series can be represented by a general formula.
6. MOLECULAR MASS
    Molecular mass of any two consecutive members differ by 14 units
7. CHEMICAL PROPERTIES
    All the members of a homologous series have same chemical properties due to same functional group.
8. METHODS OF PREPARATION
    Generally all the members of a series can be prepared by using same method.
9. PHYSICAL PROPERTIES
    Physical properties of the members of a homologous series vary with the increase in atomic weight.

(v) How to differentiate alkane from alkene

(vi) comparing combustion of alkane and alkene

All carbon compound combust in excess oxygen to produce CO₂ and H₂O

Alkene burns with more sooty flame than corresponding alkane due to higher % of carbon by mass.


(vii) inter conversion of alkane, alkene, alcohol, carboxylic acid and ester
        After learning carbon compound, you should be able to state name of reaction,
        conditions of reaction and write balanced chemical equation for the chemical
        reaction involving carbon compounds.

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Carbon compounds - download this short note to help you to score in this topic.
(link updated 9/9/2012)