Organic Chemistry: Some Basic Principles and Techniques NCERT Textbook PDF

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Organic Chemistry

Chapter 12: Organic Chemistry Some Basic Principles and Techniques

12.1 General Introduction

Organic compounds are vital for sustaining life on earth and include complex molecules like genetic information bearing deoxyribonucleic acid (DNA) and proteins that constitute essential compounds of our blood, muscles, and skin.

Organic chemicals appear in materials like clothing, fuels, polymers, dyes, and medicines.

These are some of the important areas of application of these compounds. The science of organic chemistry is about two hundred years old.

Around the year 1780, chemists began to distinguish between organic compounds obtained from plants and animals and inorganic compounds prepared from mineral sources.

Berzelius, a Swedish chemist proposed that a ‘vital force’ was responsible for the formation of organic compounds.

However, this notion was rejected in 1828 when F. Wohler synthesized an
organic compound, urea from an inorganic compound, ammonium cyanate.

12.2.1 The Shapes of Carbon Compounds

The knowledge of fundamental concepts of molecular structure helps in understanding and predicting the properties of organic compounds. You have already learned theories of valency and molecular structure in Unit 4.

Also, you already know that the tetravalence of carbon and the formation of covalent bonds
by it are explained in terms of its electronic configuration and the hybridization of s and p orbitals.

It may be recalled that the formation and the shapes of molecules like methane (CH4), ethane (C2H4), and ethyne (C2H2) are explained in terms of the use of sp3, sp2, and sp hybrid orbitals by carbon atoms in the respective molecules.

Hybridization influences the bond length and bond enthalpy (strength) in organic compounds.

The sp hybrid orbital contains more s character and hence it is closer to its nucleus and forms shorter and stronger bonds than the sp3 hybrid orbital.

The sp2 hybrid orbital is intermediate in s character between sp and sp3 and, hence, the length
and enthalpy of the bonds it forms are also intermediate between them. The change in hybridization affects the electronegativity of carbon.

The greater the s character of the hybrid orbitals, the greater the electronegativity. Thus, a carbon atom having an sp hybrid orbital with 50% s character is more electronegative than that possessing sp2 or sp3 hybridized orbitals.

This relative electronegativity is reflected in several physical and chemical properties of the molecules concerned, about which you will learn in later units.

AuthorNCERT
Language English
No. of Pages39
PDF Size30.2 MB
CategoryChemistry
Source/Creditsncert.nic.in

NCERT Solutions Class 11 Chemistry Chapter 12 Organic Chemistry: Some Basic Principles and Techniques

Question 12.1:

Draw formulas for the first five members of each homologous series beginning with the following compounds

(a) H–COOH

(b) CH3COCH3

(c) H–CH=CH2

Answer 12.6:

The first five members of each homologous series beginning with the given compounds are

(a)

H–COOH: Methanoic acid

CH3–COOH: Ethanoic acid

CH3–CH2–COOH: Propanoic acid

CH3–CH2–CH2–COOH: Butanoic acid

CH3–CH2–CH2–CH2–COOH: Pentanoic acid

(b)

CH3COCH3: Propanone

CH3COCH2CH3: Butanone

CH3COCH2CH2CH3 : Pentan-2-one

CH3COCH2CH2CH2CH3: Hexan-2-one

CH3COCH2CH2CH2CH2CH3 : Heptan-2-one

(c)

H–CH=CH2: Ethene

CH3–CH=CH2: Propene

CH3–CH2–CH=CH2: 1-Butene

CH3–CH2–CH2–CH=CH2: 1-Pentene

CH3–CH2–CH2–CH2–CH=CH2: 1-Hexene

Question 12.2:

What are electrophiles and nucleophiles? Explain with examples.

Answer 12.2:

A nucleophile is a reagent that has an electron pair and is willing to donate it. It is also known as a nucleus-loving reagent. Ex: NC, OH, R3C (carbanions), etc.

An electrophile is a reagent that is in need of an electron pair and is also known as an electron-loving pair. Ex: Carbonyl groups, CH3CH2+(Carbocations), Neutral molecules (due to the presence of electron deficiency atom).

Question 12.3:

Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles:

(a) CH3COOH + HO\rightarrow→ CH3COO + H2O

(b) CH3COCH3+ CN \rightarrow→ (CH3)2C(CN) + (OH)

(c) C6H5 + CH3C+O \rightarrow→ C6H5COCH3

Answer 12.3:

A nucleophile is a reagent that has an electron pair and is willing to donate it. It is also known as a nucleus-loving reagent.

An electrophile is a reagent that is in need of an electron pair and is also known as an electron-loving pair.

(a) CH3COOH + HO\rightarrow→ CH3COO + H2O

It is a nucleophile since HO- is electron-rich in nature.

(b) CH3COCH3+ CN \rightarrow→ (CH3)2C(CN) + (OH)

It is a nucleophile since CN is electron rich in nature.

(c) C6H5 + CH3C+O \rightarrow→ C6H5COCH3

It is an electrophile since CH3C+O is electron-deficient in nature.

Organic Chemistry: Some Basic Principles and Techniques Textbook With Solutions PDF Free Download

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