Organic Chemistry Some Basic Principles and Techniques Notes Class 11

In this unit, we will deal with the notes of Organic Chemistry Some Basic Principles and Techniques of Class 11 Chemistry. The chapter has been divided into two units. This unit (Part 1) is on the Classification of organic compounds and Nomenclature of Organic Compounds. The second unit (Part 2) is on Isomerism and Stereoisomerism.

ORGANIC CHEMISTRY – SOME BASIC PRINCIPLES AND TECHNIQUES (PART 1) NOTES

Organic chemistry is the study of most carbon compounds with the exception of a few (e.g., CO₂ and carbonate salts). While inorganic chemistry deals with the study of all other compounds.

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CLASSIFICATION OF ORGANIC COMPOUNDS: Basic Principles Of Organic Chemistry 

Classification of organic compounds is basically based on the functional group. The chemical properties of the compound depend on the properties of the functional group present in it. The rest of the molecule simply affects the physical properties, e.g., m.p., b.p., density etc. and has very little effect on its chemical properties.

They are classified as follows:

(i) Acyclic or open-chain compounds: These compounds are also called as aliphatic compounds in which all the carbon atoms are linked to one another to form open chains (straight or branched). These may be either saturated or unsaturated. For example,

 (ii) Cyclic or closed-chain compounds: It contains at least one ring or closed chain of atoms. The compounds with only one ring of atoms in the molecule are known as monocyclic but those with more than one ring of atoms are termed as polycyclic.

 

(iii) Alicyclic compounds: These are the compounds which contain rings of three or more carbon atoms. These resemble with aliphatic compounds than aromatic compounds in many respects. Some of the examples are,

 

(iv) Aromatic compounds: These compounds consist of at least one benzene ring, i.e., a six-membered carbocyclic ring having alternate single and double bonds. Generally, these compounds have some fragrant odour and hence, named as aromatic.

These are also called benzenoid aromatics.

(v) Non-benzenoid aromatics:

(vi) Alicyclic heterocyclic compounds: Heterocyclic compounds which resemble aliphatic compounds in their properties are called Alicyclic heterocyclic compounds. For example

(vii) Aromatic heterocyclic compounds: Heterocyclic compounds which resemble benzene and other aromatic compounds in most of their properties are called Aromatic heterocyclic compounds. For example,

FUNCTIONAL GROUP 

A functional group is an atom or group of atoms in a molecule that gives the molecule its characteristic chemical properties. Double and triple bonds are also considered as functional groups.

Homologous Series

Organic compounds containing one particular characteristic group or functional group constitute a homologous series, e.g., alkanes, alkenes, haloalkanes, alkanols, alkanals, alkanones, alkanoic acids amines etc.

NOMENCLATURE OF ORGANIC COMPOUNDS

Trivial or Common Names

In the earlier days, because of the absence of IUPAC names, the names of the compounds were dependent on the source from which the compound was obtained. Even today, in spite of IUPAC nomenclature some of the common names are still at use. In some case, where the IUPAC name is very tedious we prefer to use common names, for example, lactic acid, sucrose etc.

IUPAC Names

The IUPAC nomenclature of organic compounds is a systematic method of naming organic compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). This system uses substitutive nomenclature, which is based on the principal group, and principal chain. The IUPAC rules for the naming of alkanes from the basis of the substitutive nomenclature of most other compounds –

IUPAC and Common Names of Some Functional Groups and Classes of Organic Compounds: Short Notes on the Basic Principles of Organic Chemistry Class 11

IUPAC Rules for Saturated Hydrocarbons

1.Alkanes:

General formula: C_nH_2n+2

IUPAC group suffix: – ane

2. Alkenes:

General Formula: C_nH_2n ⇒ suffix –ene3. Alkyne:

General formula: C_nH_{2n – 2} ⇒ suffix –yne

Functional group structure:

4. Halides:

General formula: C_nH_2n+1 X (X = F, Cl, Br, I) (RX) suffix = Halo

Functional group structure – X

5. Alcohols:

General formula: C_nH_2n+1 OH (R – OH)

IUPAC suffix: – ol;  Common name = Alcohol;   IUPAC prefix: – Hydroxy.

Functional group structure: – OH

Example  CH3OH     IUPAC name    Methanol    Common name      Methyl alcohol or Carbinol or Zerone

6. Carboxylic acids:

General formula: C_nH_2n+1 COOH (R – COOH)

IUPAC suffix: -oic acid; Common name = Acid; IUPAC prefix : – Carboxy

Functional group structure: (–COOH)

7. Aldehydes:

General formula: (R – CHO)

IUPAC suffix: – al; Common name = Aldehyde; IUPAC prefix: Formyl or oxo-

Functional group structure: (–CHO)

8. Ketones:

General formula: R₂C = O

IUPAC suffix: – one; Common name – Ketone; IUPAC prefix; – oxo,

9. Nitriles:

General formula: C_nH_2n+1 CN (R – C ≡ N)

IUPAC suffix: nitrile; Common name: Cyanide; IUPAC prefix: Cyano

Functional group structure: ( – C ≡ N)

10. Ethers:

General formula: (R – O – R’)

IUPAC suffix: — Common name: (Ether)

IUPAC prefix: alkoxy (smaller chain) alkane (larger chain)

Functional group structure: (R – O – R’)

Example: CH₃ – O – CH₃ or (CH3)₂O or Me₂O 

IUPAC name: Methoxy methane Dimethyl ether

11. Esters:

General formula: 

IUPAC suffix: -oate IUPAC prefix: alkoxy carbonyl

Functional group structure: (–COOR)

12. Acyl halides:

General formula: (R – CO – X) (X = F, Cl, Br, I)

IUPAC suffix: -oyl halide; IUPAC prefix: halocarbonyl

Functional group structure: 

13. Amides:

General formula: 

IUPAC suffix: amide;   IUPAC prefix: Carbamyl

Functional group structure:

14. Anhydrides:

General formula: 

IUPAC suffix: – oic anhydride; IUPAC prefix: Acetoxy or acytyloxy

Functional group structure: (–COOCO–)

15. Acid hydrazides:

General formula: 

IUPAC suffix – hydrazide;  IUPAC prefix: —

Functional group structure: (–CONHNH₂ )

16. Acid azides:

General formula: 

IUPAC suffix: azide

Functional group structure: (–CON₃)

17. Thioalcohols or Thiols or Mercaptans:

General formula: (RSH)

IUPAC suffix: thiol; IUPAC prefix: mercapto

Functional group structure: (–SH)

Example: CH₃SH or MeSH 

IUPAC name: Methanethiol

Common name (derived from acid): Methyl thioalcohol or Methylmercaptan

18. Thioethers:

General formula: (R – S – R)

IUPAC suffix: thioether;    IUPAC prefix: —

Example: CH₃SCH₃ ore MeSMe or Me₂S

IUPAC name: Methyl thioether or (Methyl thio) Methane

Common name (derived from acid): Dimethyl sulphide

19. Amines:

General formula:

IUPAC suffix: amine; IUPAC prefix: amino

Functional group structure: –NH₂, (1º), >NH (2º), >N – (3º)

20. Nitro compounds:

General formula: (RNO₂)

IUPAC suffix: — ; IUPAC prefix: nitro

Functional group structure: (–NO₂)

Example: CH₃NO₂

IUPAC name: Nitromethane

21. Alkyl nitrites:

General formula: (R – O – N = O)

IUPAC suffix: nitrite

Functional group structure: (–O–N=O)

Example

i. CH₃ – ONO or Me – O – N = O

IUPAC Name: Methyl nitrite

ii. CH₃CH₂CH₂ONO or Pr – O – N = O

IUPAC Name: Propyl nitrite

22. Alkyl isocyanides or Isonitriles:

General formula: 

According to an IUPAC recommendation the substituent – NC is termed as carbylamino. Thus, CH₃NC is carbylamino methane and so on. However, this name is not in use. For naming isocyanides, iso is prefixed to the name of the corresponding cyano/nitrile compound. In another mode, the suffix carbylamine is added to the name of the alkyl group

Example: CH₃NC

Common name: Methyl isocyanide or Acetoisonitrile or Methyl carbylamine

23. Sulphonic acids:

General formula: (R – SO₃H)

IUPAC suffix: sulphonic acid                          IUPAC prefix: sulpho

Functional group structure: (R – SO₃H)

24. Imines:

General formula: RCXH = NH

IUPAC suffix: imine                       IUPAC prefix: None

Functional group structure: (–CH = NH)

Example: HCH = NH

IUPAC name: Methanalimine

Common name: Formaldimine

25. Cyclic ethers:

General formula: O atom

IUPAC suffix: —                             IUPAC prefix: epoxy

IUPAC Rules for Saturated Hydrocarbons: Organic Chemistry Notes For Class 11

(a) Select the longest possible chain (parent chain). The chain should be continuous.

(b) C atoms which are not included in this chain are considered substituents (side chain).

(c) In the case of two equal chains having the same length, the one with the larger number of side chains or alkyl groups is selected.

(d) The numbering of C atoms in the parent chain starts from that end where the substituent acquires the lowest position numbers or locant.

(e) Lowest sum rule: In the case of two or more substituents, numbering is done in such a way that the sum of position number substituent or location is the lowest.

(f) Position and substituent name are separated with a case (-)

(g) In case of more than one substituent, they are prefixed by their respective locants in alphabetical order

IUPAC Rules for Unsaturated Hydrocarbons

(a)All the rules of alkanes are also applicable there.

(b) The parent or the longest chain is selected irrespective of the = or σ bonds.

(c) The numbering is done from the end which is nearer to the = bond, and according to the lowest sum of the locant rule.

(d) The numbering or sum rule will follow the alphabetical order of the substituent.

IUPAC Rules for Functional Groups

While numbering the longest chain, the function group should acquire the lowest number followed by other substituent and the family of multiple bonds even if it violates the lowest sum rule.

IUPAC Rules for Chain Terminating Functional Groups (-CHO, -COOH, -CONH2, -COCl) in Organic Chemistry

These chain-terminating groups are included in the numbering, starting from the end where it acquires the lowest number followed by other substituents in alphabetical order.

IUPAC Rules for Polyfunctional Compounds

In the case of polyfunctional compounds, one of the functional groups is chosen as the principal functional group and the compound is named on that basis. The remaining functional group which is subordinate functional groups are named as substituents using the appropriate prefixes.

The decreasing order of priority of some functional groups is

–COOH > – SO₃H > – COOR (ester) > – COCl (acylhalide) > – CONH₂ (amide) > – C ≡ N (nitriles) > – CH = O (aldehyde)> C = O (keto) > – OH (alcohol) > – NH₂ (amine) > C = C (alkene) > – C ≡ C – (alkyne) The – R (alkyl group), Ph or C₆H₅ –(phenyl), halogens (F, Cl, Br, I) – NO₂ alkoxy (–OR). Etc., are always prefix substituents.

Thus, a compound containing both an alcohol and a keto group is named hydroxyl alkanone since the keto group is preferred to the hydroxyl group.

Notes for IUPAC Rules for Alicyclic Compounds in Organic Chemistry Class 11

1.IUPAC suffix: ane, ene, yne IUPAC prefix: cyclo

Two or more alkyl groups or other substituents are present in the ring, their positions are indicated, e.g., 1,2,3 …., etc. The substituent which comes first in the alphabetical order is given the lowest number, as per the lowest sum rule, e.g.

2. (a) If the ring contains equal or more number of C atoms than the alkyl groups attached to it, is named as an alkyl cycloalkane.

(b) If the ring contains a lesser number of C atoms than the alkyl groups attached to it, is named cycloalkyl alkane, e.g.,

(c) If the side chain constraints a functional group or multiple bonds, then the alicyclic ring is considered
substituent irrespective of the size of the ring, e.g.,

IUPAC Name of Aromatic Compounds

(a)No specific rules are required to name aromatic compounds. However, they are named substituted benzene.

(b) When larger and complex groups are attached to the benzene ring, the molecule is named as an alkane, alkene, etc., and benzene as side chain derivatives, abbreviated as, Ph –, or C₆H₅ – Ph –. When the benzene ring contains some substituent’s, it is abbreviated as Ar–.

Writing the Structural Formula from the Given IUPAC Name in Organic Chemistry 

The IUPAC name of an organic compound consists of the following parts:

1. Root word;      b. 1^o suffix;     c. 2^o suffix;     d. 1^o prefix;     e. 2^o prefix

(a) Root word indicates the longest chain thus, first locate the longest chain from the root word. Write the number of C atoms in a straight chain or in a zigzag manner (for bond line structure) and then number them from any end.

(b) 1^o suffix (-ane, -ene, or -yne) indicates the nature of the chain. Put the multiple bonds at proper places in the chain.

(c) The 2^o suffix indicates the principal functional group. Put in a proper place in the chain.

(d) Prefixes are the substituents or secondary functional groups. Put them at a proper place with the help of locants.

(e) Add H atoms to satisfy valences of each C atom if the stick formula is used. If the structure is written bond line, then there is no need of adding H atoms.

Check Part 2 of the chapter here: Organic Chemistry – Some Basic Principles and Techniques Part 2