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Basic principles and techniques in organic chemistry

Qualitative Analysis

  • A Swedish chemist named Berzilius proposed the vital force theory, according to which a vital force existing in living organisms is responsible for the formation of oranic compounds. However, this was proved to be incorrect when F. Wohler, a German chemist synthesised urea- an organic compound from ammonium cyanate, an inorganic compound.

  • Shape of carbon compounds

  • sp orbital has 50% ‘s’ character. Thus, an sp hybridised carbon is more electronegative than an sp2 (33% s character) or sp3 (25% s-character) hybridised carbon.

  • Hybridisation influences the bond length and bond enthalpy.

Some Characteristic Features of π-Bonds

  • Parallel orientation of two p-orbitals on adjacent atoms is necessary for a proper sideways overlap to form π-bond.

  • Rotation about C = C double bond is restricted.

  • Electron charge cloud of π-bond is located above and below the plane of bonding atoms.

  • Electrons are easily available to attacking reagents.

Structural Representations of Organic Compounds

  • Complete Structural Formula

Examples:

  • Condensed Structural Formula

(Structural formula obtained by omitting some or all of the dashes representing covalent bonds and then using a subscript to indicate the number of identical groups attached to an atom)

  • Bond-Line Structural Formula

  • Only lines are used to represent the structure of organic compound.

  • Carbon and hydrogen atoms are not shown.

  • Lines representing the C − C bonds are drawn in a zig-zag fashion.

  • For example − bone-line formula of 2,3-dimethylhexane can be represented as

  • In cyclic compounds,

To test your knowledge of this concept, solve the following puzzle.

  • A Swedish chemist named Berzilius proposed the vital force theory, according to which a vital force existing in living organisms is responsible for the formation of oranic compounds. However, this was proved to be incorrect when F. Wohler, a German chemist synthesised urea- an organic compound from ammonium cyanate, an inorganic compound.

  • Shape of carbon compounds

  • sp orbital has 50% ‘s’ character. Thus, an sp hybridised carbon is more electronegative than an sp2 (33% s character) or sp3 (25% s-character) hybridised carbon.

  • Hybridisation influences the bond length and bond enthalpy.

Some Characteristic Features of π-Bonds

  • Parallel orientation of two p-orbitals on adjacent atoms is necessary for a proper sideways overlap to form π-bond.

  • Rotation about C = C double bond is restricted.

  • Electron charge cloud of π-bond is located above and below the plane of bonding atoms.

  • Electrons are easily available to attacking reagents.

Structural Representations of Organic Compounds

  • Complete Structural Formula

Examples:

  • Condensed Structural Formula

(Structural formula obtained by omitting some or all of the dashes representing covalent bonds and then using a subscript to indicate the number of identical groups attached to an atom)

  • Bond-Line Structural Formula

  • Only lines are used to represent the structure of organic compound.

  • Carbon and hydrogen atoms are not shown.

  • Lines representing the C − C bonds are drawn in a zig-zag fashion.

  • For example − bone-line formula of 2,3-dimethylhexane can be represented as

  • In cyclic compounds,

To test your knowledge of this concept, solve the following puzzle.

(I) Acyclic or open chain compounds consist of straight or branched chain compounds.

(II) Alicyclic or closed chain or ring compounds contain carbon atoms joined in the form of a ring (homocyclic). In some rings (heterocyclic), atoms other than carbon are present.

Aromatic Compounds

  • Benzenoid aromatic compounds (include benzene and other related compounds)

  • Non-benzenoid compounds (do not contain benzene ring)

  • Heterocyclic aromatic compounds

Functional Group

  • An atom or group of atoms joined in a specific manner which is responsible for the characteristic chemical properties of the organic compound.

  • Examples: Hydroxyl group (− OH), carboxylic acid group (− COOH), aldehyde group (−CHO), ether group (−O−), ketone group , etc.

Homologous Series

  • A group or a series of organic compounds each containing a characteristic functional group.

  • The members of the series are called homologues.

  • Successive members differ from each other in a molecular formula by a −CH2 unit.

  • Alkanes, alkenes, alkynes, alkanoic acids, amines, etc. represent homologous series.

  • An organic compound can be named by identifying the parent hydrocarbon and the functional groups attached to it.

  • Using prefixes and suffixes, the parent name can be modified to obtain actual name.

IUPAC Name of Alkanes

  • For straight chain hydrocarbons

Prefix →indicates the number of carbon atoms (except from CH4to C4H10)

Suffix →‘ane’

  • Branched chain hydrocarbons

Rules for the Nomenclature of Branched Chain Alkanes

  • Longest chain in the molecule is identified (called parent or root chain).

  • Numbering is done is such a way that the branched carbon atoms get the lowest possible numbers.

  • The names of alkyl groups attached as a branch are then used as prefix in the name of parent chain. The position of the substituents is indicated by the appropriate numbers.

  • If two or more identical groups are present, then prefix …

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