Class XII CHEMISTRY
ORGANIC CHEMISTRY Introduction: Organic compounds play a vital role on this earth. Organic chemicals appear in materials like clothing, fuels, polymers, and dyes. Organic chemistry is around two hundred years old. The formation of acetic acid by Kolbe method showed that organic compounds could also be prepared from inorganic norganic-compounds. Page | 1 Organic chemistry is the branch of science science in which we study the properties, reactions, and uses of organic compounds. Hydrocarbons are those compounds in which a carbon atom is directly attached to hydrogen atoms. All hydrocarbons are organic compounds but not all organic compounds are hydrocarbons. All carbon compounds except for a few inorganic carbon compounds are organic. Inorganic carbon compounds include the oxides of carbon, the bicarbonates, and carbonates of metal ions, metal cyanides, and a few others. Nomenclature of Organic Compounds: There are huge numbers of organic compounds are known. One might think that the study of organic chemistry is very difficult. However it is not so because organic compounds are classified into the various families on the basis of their properties. propert Classifications of Organic compounds are divided into various classes as follows.
1. Acyclic Compounds: Compounds in which all the carbon atoms are linked to one another to form open chains(straight chain) are called acyclic, open chain or aliphatic. aliphatic. These may be saturated or unsaturated. For example, Examples: Methane 1 CH4 Methyl alcohol 2 CH3OH CH=CH2 Buta-1,3-diene 3 CH2=CH-CH=CH 2. Cyclic compounds:: Cyclic compounds which is made up of only one type of atom, the compound is known as homo-cyclic cyclic and if the ring contains one heteroatom (N, S, and O), the compound is known as heterocyclic compound.
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(a) Homocyclic compounds: these types of compounds contain ring, which are made up of only one type of atoms. The organic compounds contain of only carbon atoms, it is also known as carbo-cyclic cyclic compounds. They are divided into two partsparts (i) Alicyclic compounds: Carbocyclic compounds which resemble aliphatic compounds in Page | 2 their properties are called alicyclic compounds. These are the compounds compounds in which, the carbon atoms are joined by the covalent bonds to form the ring structures.
(ii) Aromatic compounds:: Organic compounds containing one or more fused or isolated benzene rings (a six-member member ring of carbon atoms with alternate single or double bonds) are called aromatic compounds.
(b) Heterocyclic compounds:: These are the compounds containing ring structure in which one or more carbon atoms are replaced by hetro atoms (N, S, O etc) are known as heterocyclic compounds. These are of two types: t (i) Alicyclic Heterocyclic Compounds: Heterocyclic compounds, which resemble aliphatic compounds in their properties are called alicyclic heterocyclic compounds.
(ii) Aromatic Heterocyclic Compounds: heterocyclic compounds, which resemble aromatic compounds in most of their properties, are called aromatic heterocyclic compounds or non nonbenzenoid aromatic compounds.
Functional Group or Characteristic Groups: An atom or group of atoms, which largely determines the properties of the organic compound particularly particularly the chemical properties, is called a Functional group. Organic compounds are classified into various families on the basis of their properties most of the organic compound can be divided into two parts (a) Reactive part called functional group. (b) A Skelton of carbon and hydrogen atoms, which is called as alkyl or aryl group. The properties of the compounds are generally controlled by functional groups. For example- The properties of Ethyl alcohol (C2H5OH) and Ethylamine (C2H5NH2) are different though their alkyl radicals are same. The difference in properties due to the different www. shinehill.in
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functional group attached to the alkyl chain. The –OH and –NH2 groups are the functional groups of alcohols and amines respectively. Homologous Series: A series of closely related organic compounds, which can be represented by a general formula, is called Homologous Series. Characteristics of Homologous Series: All member of a series can be represented by a general formula.
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IUPAC Name General Formula S.No. Alkane CnH2n+2 1 Alkene CnH2n 2 Alkyne CnH2n-2 3 Alkyl CnH2n+1 4 • All members obey the same general formula. • Every successive member differs by a methylene (-CH ( 2-) group. • They have ve similar chemical properties. • Their physical properties such as melting point, boiling point, density, solubility etc shows the regular gradation with the increase in molecular mass. Nomenclature of Organic Compounds: - There are two methods by which naming of organic compounds are done. (A) TRIVIAL SYSTEM: - In this system, compounds are named after the source from which they are obtained. Some compounds and their sources are given below: Compound NH2CONH2 HCOOH CH3COOH CH3 CH2 CH2COOH
Name
Source
Urea Formic Acid Acetic acid Butyric acid
Urine Formica (ant) Acetum(sour) Butyrum (butter)
(B) IUPAC SYSTEM: The nomenclature of the organic compounds is done by the systematic nomenclature system given by IUPAC in 1950. The most widely used system is substitutive nomenclature. The substitutive name of an organic compound is based on its principal group and principal chain. IUPAC: - “International Union of Pure and Applied Chemistry”. The IUPAC compounds contains three parts namely-
Root Word- This is the basic unit, which indicate the carbon chain in the molecule structure. It tells us the number of carbon atoms in the principle chain. Depending upon the numbers of Carbon atoms the root words are as follows:
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Suffix:: Suffix is added indicating the saturated or unsaturated nature of the parent chain and the functional group present in the molecule. There are two types of Suffixes(i) Primary Suffix (ii) Secondary Suffix (i) Primary Suffix: - It tells the linkage between the carbon atoms.
(i) Secondary Suffix: It tells the characteristic functional group present in the organic compound. It is added to the name, after the primary suffix. Some common secondary suffixes are given below.
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Note- When we are using these secondary suffixes, the carbon of the functional group (if any) is counted in the principle chain. Prefixes:: The prefix depends upon the carbon atom present in a parent chain.
Prefix indicates the substituent of other atoms or groups in place of hydrogen atom in the main chain of carbon bon atoms. Most commonly used prefixes are alkyl groups and groups or atoms, which are not regarded as principle functional groups. Some of these prefixes are given below.
For Alcohol Group (OH) – e ---- ol- Alkane in place of “e” - “ol” will come.
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For example-
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For Ether Group (ROR) – Small group group-Oxi /Oxy and the remaining group-Alkane Alkane
Nomenclature of saturated branched hydrocarbons: Position of Locants: A locant is numeral (1, 2, 3….) or a letter (o, m, pp- etc) used to locate the position of a substituents or a carbon-carbon carbon carbon multiple bond. These locants are placed immediately before the part of the name of which they relate. For example, according to www. shinehill.in
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IUPAC names to the latest rules for Pent-2-ene, Pent name like Pentene-2 or 2-Pentene Pentene are not correct. Numerical Prefixes: Numerical prefixes are used to describe a multiplicity of identical feature of a structure in chemical nomenclature. These are derived from Greek or Latin number names. Some common numerical prefixes are given below. Page | 7
Numerical ical prefixes such as ‘bis’, ‘tris’, ‘t tetrakis etc are used to indicate a multiplicity of a substituted substituents.
Bracket or Parenthesis: The brackets or Parenthesis is used around round prefixes defining substituents after the numerical multiplicative prefix, if any. Use of Hyphen: The use of hyphen, brackets, and numerical prefixes are illustrated in the following examples; A hyphen separates a locant from the words of the name. F For example, -A
Nomenclature of simple alkanes: The names of first ten alkanes are given in the following tables: -
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Nomenclature of branched alkanes: 1. Selection of Parent chain: Rule1: - Select the longest continuous chain of carbon atoms as a parental (principal) chain. All other carbon atoms, which are not included in this chain, are regarded as substituents and denoted as prefixes. Example: -
The given alkane is named as a derivative of the alkane representing the parent chain. It is noted the longest chain may or may not be straight but it must be continuous.
Rule2: - If two and more than two longest chains are the present in the compound then the chain having larger number mber of side chains will be principal chain.
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The chain (written in blue color) has side chains at 2, 3, 4, 5 carbon atoms, while the chain (written in pink color) has side chains at 2, 3, 4 carbon atoms. Therefore, longest chain will be the chain named in blue color. Rule3: - Numbering of the Principle Chain: (Lowest Number of Rule): The selected carbon chain is numbered from the end nearest to the side chain or substituents to give the Page | 9 lowest no. to the carbon having the side chain. The sums of the number assigned to the substituents are mini-mum. mini Locant is used to denote the number indicating the substituents attached. attached
In the above structure, if we start the numbering from left hand-side, hand then substituted group comes at carbon number-55 while if we do the numbering from the right-hand right hand side, then substituted group comes at carbon-number-3. carbon 3. Therefore, Numbering from right hand side is correct.
From the above figure, it is clear that in figure-2 figure the lowest set of locant is applicable. Rule 4: - Numbering Same Substituents at Different Position Position:: When the same substituents occurs more than one time in a parent chain, the positional number of each substituents is separated by commas and suitable numerical numerical prefixes such as di, tri, tetra, etc., are attached to the same. In case the same substituents occur twice on the same carbon atom, its positional number is repeated twice with a comma in between.
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In this structure, methyl group is repeated thrice, so in the naming of the structure, we have used tri before methyl. Rule5: - Alphabetic Order of Substituents: If more than one group attached to the carbon chain, they should be arranged alphabetically. While deciding alphabetical order of simple substituents numerical affixes such as di, tri, tetra – etc (if any) are not considered. When two or more identical substituents are present prefix prefix- di, tri, tetra- etc are used. The position of substituents is separated by commas Example: -
Such substituted substituents or Rule6: - Naming of Univalent Branched Chain Radicals: Such complex radicals are derived from the name of the alkane representing the longest chain. The numbering should be done in the way that the carbon atom with free valence gets number 1.
Note: IUPAC has retained following semi systematic names for branched chain alkanes, provided they are not substituted. However, these semi systematic names are not yet widely accepted in IUPAC nomenclature.
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Special Case of Nomenclature of Branched Chain Alkanes: Al 1. Deciding the Order of complex substituents: Complex radicals are alphabetized under the first letter of their complete names i.e., including the numerical affix (if any). This is clear from the following compounds. Page | 11
Here dimethylpropyl as a complex single substituents is alphabetized under‘d’ and as such written before ‘e’ of ethyl. In the case where the names of complex radicals are composed of identical words priority is decided by considering the locants in the complex radicals. For example,
In second figure, numbering of the carbon atoms is done in wrong way. At carbon number number-5, the attached group has substitute at carbon-2, carbon while at carbon-number-6, 6, the attached group has substitute (methyl) at carbon-1. carbon 1. We know that, numbering should be do done from the lowest locant side. 2. Numbering of Different Substituents at Equivalent Positions Positions:: When two different substituents are present at equivalent positions, the numbering of parent chain is done in such a way that the substituent, which comes firstt in the alphabetical order gets the lower number. For example-
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In this example, ethyl is written before methyl group because ‘E’ comes before ‘M’. 3. Deciding the Principal Chain When there are two or More Chains of Equal Lengths Lengths: When there are two orr more chains of equal length, then the chain with greater number of side chains as substituents should be selected as principal chain for example,
In case if there are two or more chains of equal lengths have the same number of side chains, then the chain whose side chain have the lowest numbered locants is selected as principal chain. For example,
Here the set of locant s 2, 4, 5 is lower than the th set 2, 4, 6 Example1: -Name Name the following compound using IUPAC substitutive nomenclature?
Solution: Principle chain contain 7 carbon atoms, hence it is substituted heptane. The branches are at C-22 with methyl group and C-4 C with ethyl group. According to IUPAC, rules if more than one group attached to the carbon chain, they should be arranged alphabetically, and the sum of the number assigned to the substituents are minimum. It is 4-Ethyl-2-methyl-heptane. heptane. Some important tips: 1. Branching group are generally termed as substituents. substitu The name of an un un-branched alkyl substituent is derived by replacing ‘ane’ by ‘yl’. www. shinehill.in
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2. The prefix n-(normal) (normal) refers to a straight chain alkyl group. If the name does not have Page | 13 prefix ’n’, it is assumed that carbon carb atoms are in continuous chain.
3. The prefix-iso iso refers that a straight chain contains one methyl group at second carbon from the opposite end.
4. The prefix-‘neo’ ‘neo’ is used when a carbon is attached to three other carbons. It is used mainly in pentane.
5. The prefix-‘s’ ‘s’ is used when a carbon carbo is attached to two other carbons. 6. The prefix-‘t’ ‘t’ is used when a carbon is attached to three other carbons.
7. An acyclic bridge is named as a prefix derived from the hydrocarbon name by changing the final ‘e’ to ‘o’. The position of a double bond, if present is indicated in square brackets between the hydrocarbon prefix and the ending ‘-eno’ ‘ eno’ or ‘-dieno’, ‘ etc. Compound structure -CH2-CH2-CH2-CH=CH-CH=CH-CH2 -CH2-CH=CH-CH2-CH=CH-CH=CH-
Name Methano Ethano Etheno Pro[1]eno But[2]eno Buta [1,3]dieno
Nomenclature of acyclic or heterogeneous bridge: -
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Important: Common names that you should know are... isopropyl = 1-methylethyl isobutyl = 2-methylpropyl sec-butyl = 1-methylpropyl tert-butyl = 1,1-dimethylethyl neo-pentyl = 2,2-dimethylpropyl dimethylpropyl iso-pentyl = 3-methylbutyl Example2: - Name the following compound using the IUPAC nomenclature.
(a) 4-propylheptane (c) 2-methyl-3-propyl propyl hexane
(b) 4-(1-methylethyl) heptanes (d) 4-propyl-5-methyl hexane
Answer: - (b)
The principal chain contains seven carbons; hence, it is substituted as heptane.. At carbon carbon-4, we have a branch of three carbons. This branch is called isopropyl or 1-methylethyl. 1 Therefore, name of the compound is 4-(1-methylethyl)heptane Example3: - Name the following compound using the IUPAC nomenclature.
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(a) (b) (c) (d)
2,4-dimethyl-5-propylheptane propylheptane 5-propyl-2,3-dimethylheptane dimethylheptane 2,4-dimethyl-5-ethyloctane ethyloctane 5-ethyl-2,4-dimethyloctane dimethyloctane
Answer: - (d)
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The principal chain contains eight carbons; hence, it is substituted as octane. There are three branches is attached to the principal chain. Two branches are methyl group and one branch is ethyl group. ethyl-2, 4-dimethyloctane The name of the compound is 5-ethyl (Ethyl will come before methyl) Example4: - Name the following compound compounds using the IUPAC nomenclature.
Answer:(A) The IUPAC name of the compound is 3,3-dimethylhexane 3,3
(B) The name of the compound is 4-(1,1-dimethylethyl)-heptane 4
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(C) The name of the compound is 5-ethyl-3-methyl-4-(1-methylethyl)-nonane nonane
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Example5: - IUPAC name of neo neo-pentane is Answer: -
IUPAC name is 2,2-dimethylpropane dimethylpropane Example6: - Find out the primary, secondary, tertiary, and quaternary carbon in the following compound.
Answer: Type of carbon Primary Secondary Tertiary Quaternary
Position 1,9,11 2,3,5,8 6,7, 10 4
Example7: - Write the IUPAC name of the following compound?
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Answer: -
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IUPAC name is 5,6-diethyl-3-methyldecane methyldecane
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