Introduction to Organic Chemistry

CONTENT

• Unique Nature of Carbon.
• Characteristics Features of Organic Compounds
• Classification of Hydrocarbons.
• Definition of Terms used in Organic Chemistry

Organic chemistry is the chemistry of carbon compounds with the exception of compounds such as carbon (II) oxide, carbon (IV) oxide the trioxocarbonate (IV).Carbon has unique ability to form numerous organic compounds because it has ability to catenate. Catenation is the ability of atoms of an element to form bonds between its own atoms and produce long chain structure.

All organic compounds contain carbon as the main element together with one or more other elements such as hydrogen, oxygen, chlorine, nitrogen and sulphur.

UNIQUE NATURE OF CARBON

1. The valency of carbon: the electronic configuration of carbon is as follows:

C = 6: 1s² 2s¹ 2p_x¹ 2p_y¹ 2p_z¹

            Carbon form covalent bonds and after bond formation it has neither vacant orbital nor lone pair of electrons. This makes many carbon compounds chemically stable.

• The bond between carbon and hydrogen is non-polar. Thus, hydrogen atoms attached to carbon do not weaken carbon-carbon bonds.
• The types of orbital hybridization available to carbon: carbon can form three types of hybridizations: SP3, SP2 and SP hybridization. Hence, it has ability to form single, double or triple covalent bonds between its atoms.
• Large amount of energy is required to break carbon single bond.

CHARACTERISTICS FEATURE OF ORGANIC COMPOUNDS

1. Organic compounds are covalent in nature.
2. They are non-polar substances and are insoluble in polar solvents.
3. They have low melting and boiling points.
4. They are highly flammable.
5. Their reactions are relatively slow compared to inorganic chemical reactions.

CLASSIFICATION OF ORGANIC COMPOUNDS

Organic compounds are classified into Aliphatic and Aromatic compounds.

Aliphatic Compounds: These are compounds whose molecules are composed of chains of carbon atoms. They can be

1. Straight chain compounds e.g  pentane
2. Branched chain compounds e.g 2-methylbutane

Straight and branched chain aliphatic compounds exist as open chain and are called ACYCLIC compounds. Aliphatic compounds which exist as closed chain are called the CYCLIC compounds e.gcyclo propane.             

Aromatic Compounds: Benzene, C₆H₆, is a typical aromatic compound. Other aromatics compounds are derivatives of benzene e.g C₆H₅OH.

EVALUATION

1. List four reasons why carbon forms numerous organic compounds
2. State five characteristic features of organic compounds.

DEFINITION OF TERMS USED IN ORGANIC CHEMISTRY

HOMOLOGOUS SERIES

Homologous series is a family of organic compounds which follows a regular structural pattern and in which each successive member differs in its molecular formula by –CH₂– group.

The simplest series of compounds in organic chemistry is the Alkane series. The general molecular formula of the alkane series is C_nH_2n+2. It is the parent series from which every other series is obtained. Other homologous series include the Alkenes, Alkynes, Alkanols, Alkanoic acids, etc.

CHARACTERISTICS OF HOMOLOGOUS SERIES

1. All members conform to general molecular formula , e.g for alkanes, C_nH_2n+2
2. Each successive member differs in molecular formula by – CH₂– group.
3. All members undergo similar chemical reactions.
4. The physical properties of members change gradually along the series.
5. All members are prepared by the same method.

ALKYL AND FUNCTIONAL GROUPS

Alkyl groups: Alkyl groups are all groups derived from the alkanes by the loss of a hydrogen atom. Alkyl groups have a general formula of CnH₂n+1.They are named after the parent alkane by replacing the ending –ane by –yl. The alkyl group derived from the first two members of the parent alkane series are:

    Parent alkane                         Alkyl group                          Formula

     Methane, CH₄                       Methyl                                   -CH₃

     Ethane, C₂H₆                        Ethyl                                      -C₂H₅

Functional groups: The substituent of hydrogen atom in the alkane series to form the alkyl group determines the chemical properties of the compound formed thereafter. This substituent is called FUNCTIONAL GROUP.

A functional group is an atom, a radical or a bond common to a homologous series and which determines the chemical properties of the series.

Examples of functional groups include: Hydroxyl group -OH, amino group NH₂, carboxyl group -COO, double and triple bonds.

Alkyl group in a compound determines the physical properties of the compound; while functional group determine the chemical properties of the compound.

EVALUATION

1.       Define a homologous series.

2.       Define a functional group and give two examples.

SATURATED AND UNSATURATED COMPOUNDS

Saturated compounds are compounds containing atoms joined together by single covalent bond. Alkanes are saturated compounds, e.g ethane, C₂H₆

FORMULAE OF ORGANIC COMPOUNDS

Organic compounds are characterized by the following formulae

1.       Empirical formula

2.       Molecular formula

3.       Structural formula

-Empirical Formula is the simplest formula which indicates the component elements and ratio of combination of atoms in a compound.

– Molecular Formula is a chemical formula of a compound which indicates the actual number of atoms of each element in a compound.

-Structural Formula is a formula which indicates how atoms are arranged within the molecule of a substance.

Structural formula can be

1. Open structural formula
2. Condensed structural formula

GENERAL EVALUATION/REVISION

1. Differentiate between saturated and unsaturated compounds.
2. Write the open and condensed structural formula of pentane[C₅H₁₂]_.
3. Define the following terms: Homologous series and functional group.
4. Determine the oxidation number of Cl in each of the following compounds and give the IUPAC name of the compound (a) NaOCl (b) KClO₃
5. Split the following redox equations into oxidation and reduction half equation (a) Cu_(s) + 2Ag⁺_(aq) → Cu²⁺_(aq) + 2Ag_(s)

                (b) Cl_2(g) + 2I^–_(aq) → 2Cl^– + I_2(s)

Introduction to Organic Chemistry video:

READING ASSIGNMENT

New School Chemistry for Senior Secondary School by O .Y. Ababio (6^th edition), pages 514-520

WEEKEND ASSIGNMENT

SECTION A: Write the correct option ONLY.

1. Exceptional large number of carbon compounds is essentially due to the ability of

(a). carbon to catenate liberally (b).various groups to catenate

(c). nitrogen, hydrogen, phosphorus and the halogens to catenate with themselves

(d). hydrocarbons to dominate other groups.

• Which of the following is not a characteristics feature of organic compounds?

(a). Covalent in nature (b). They dissolve in all polar solvents (c).Low melting and boiling points (d).Highly flammable

• Functional groups in organic compounds (a).determine the chemical properties of the homologous series (b).does not modify the other when they are more than one in a molecule (c).have a general formula which may include the functional group (d). are responsible for the physical properties.
• Homologues have the same (a).empirical formula (b).structural formula (c).general formula (d). molecular formula
• The four main classes of hydrocarbons are (a).methane, ethene, ethyne and benzene(b).ethane, ethene, ethyne and toluene (c).cycloalkane, cycloalkene, alkynes and arenes(d). alkanes, alkenes, alkynes and aromatics

SECTION B

1. Define the following terms: a. Functional group b. Homologous series
2. Write the open chain structure of the following
3. CH₃C(CH₃)₂CH₂CH(CH₃)CH₂CH₃
4. (CH₃)₂CHCH₂CH(CH₂Cl)CH₃
5. CH₃C(Br)₂CH₂CH₃