Basics of

Organic Chemistry A Handbook for High School Students

Chandan Sengupta

Handbook Series i

Basics of Organic Chemistry A Handbook for High School Students

ISBN 978-1-68563-058-4

This publication is a part of an extended series titled Creative Commons. This book is for students having affinity towards personal advancement through series of practices. It also enables a learner of the same faculty to ascertain one’s progress in the field of Science and Technology. It also encompasses a learner for sorting out various problems related to their understanding of the subject matter. If answers are provided alongside the questions then the material will fulfill half of the purpose. It cannot contingent for overcoming the problems and also cannot facilitate in skill enhancement efforts. Set of questions can be used for the purpose of assessing skill acquisition process and also can be assigned to the ward by parents and guides. It is not mandatory to go through all sets of problems, but not to skip any of the problems is recommended for assuring the perfect skill acquisition. Organic Chemistry is the field of science which is growing day by day due to incorporations of several synthetic compounds and industrial applications in our daily life. Most prominent of all these faculties is the faculty medicine and pharmaceutical applications. Several medicines are enriching the enlisted drug availed to a doctor. They are also learning a lot during their intensive studies of medicines. Some of such studies are of greater applications and some other such studies are yet to be implemented. The present collection of questions, answers and worksheets related to organic chemistry are meant exclusively for attending the ever growing concerns of a student having affinity to opt for pre medical entrance examinations. Republishing any content of this book will be a subject matter of receiving prior concern of the author. Without taking such concern one should not go for reproducing any part of the content. For any kinds of information regarding this publication one can contact: Chandan Sengupta, Arabinda Nagar, Bankura – 722101 (WB) India Email: [email protected]

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Contents Foreword........................................................................................................................................ vii Fundamentals ................................................................................................................................. ix Properties of Carbon ....................................................................................................................... xi Hydrocarbons ............................................................................................................................... xxiii 1. Evaluation Papers......................................................................................................................... 1 Evaluation I .................................................................................................................................. 1 Evaluation II ................................................................................................................................. 5 Self Study A .................................................................................................................................. 8 Self Study B ................................................................................................................................ 10 Self Study C ................................................................................................................................ 12 Self Study D ................................................................................................................................ 13 Self Study E................................................................................................................................. 10 2. Organic Reactions ...................................................................................................................... 13 Wurtz Reaction .......................................................................................................................... 13 Aldol Reaction and Condensation.............................................................................................. 14 Cannizzaro reaction ................................................................................................................... 15 Clemmensen Reduction ............................................................................................................. 19 Fittig Reaction ............................................................................................................................ 19 Friedel-Crafts alkylation ............................................................................................................. 19 Grignard Reagents ..................................................................................................................... 22 Williamson's synthesis ............................................................................................................... 25 3. Partly Solved Papers................................................................................................................... 33 Paper I ........................................................................................................................................ 33 Paper II ....................................................................................................................................... 38 Paper III ...................................................................................................................................... 40 Paper IV ...................................................................................................................................... 43 Paper V ....................................................................................................................................... 45 4. Fact Finder ................................................................................................................................. 47

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Sheet 1 ....................................................................................................................................... 47 Sheet 2 ....................................................................................................................................... 48 Sheet 3 ....................................................................................................................................... 51 Sheet 3 ....................................................................................................................................... 54 Sheet 4 ....................................................................................................................................... 58 Sheet 5 ....................................................................................................................................... 60 Sheet 6 ....................................................................................................................................... 61 5. Acids, Esters and Ethers ............................................................................................................. 65 Carboxylic Acids ......................................................................................................................... 65 Esters.......................................................................................................................................... 69 Ethers ......................................................................................................................................... 71 Practice Papers........................................................................................................................... 72 Important Questions .................................................................................................................. 73 Self Study ................................................................................................................................... 74 Achiever Section ........................................................................................................................ 76 Model Papers ................................................................................................................................. 81 Model Paper 1 ............................................................................................................................ 81 Model Paper 2 ............................................................................................................................ 85 Model Paper 3 ............................................................................................................................ 90 Model Paper 4 ............................................................................................................................ 92 Exemplar: Carbon and its Compounds....................................................................................... 94 Model Paper: Basic Concepts .................................................................................................... 95 Model Paper: Hydrocarbons .................................................................................................... 102 Model Paper: Basic Principles and Techniques........................................................................ 118 Model Paper: Pollution ............................................................................................................ 126 Model Paper: Ecosystem ......................................................................................................... 127 Model Paper: Halo alkanes and Halo-arenes........................................................................... 145 Model Paper: Alcohols, Phenols and Ethers ............................................................................ 150 Model Paper: Aldehydes Ketones and Carboxylic Acid ........................................................... 154 Model Paper: Basic Principles and Techniques........................................................................ 159 Model Paper: General .............................................................................................................. 162 Model Paper: General II ........................................................................................................... 167 iv

Model Paper: General III ......................................................................................................... 169 Model Paper: General IV ......................................................................................................... 173 Model Paper: General V .......................................................................................................... 175 Model Paper: General VI ......................................................................................................... 181 Model Paper: General VII ........................................................................................................ 186

Foreword A book can provide timely relevant support to students. It can even equip a student differently for making oneself fit for accepting challenges of some broad spectrum. This collection is exclusively meant for students aspiring for examinations of Standard 10th . It can also provide adequate references to students aspiring for various competitive examinations. The collection of this series is coming in accord to the subject areas. Basic Science is the field of study which is common for most of the competitive examinations. The general understanding on the theories and their applications is the general expectation of examiners from a student of school education. One should understand the application of scientific temperaments for solving day to day problems. Ecology and environment is the common core of content areas for all possible levels of discussions related to science and scientific observations. For Students We expect a kind of understanding from students of Grade 10 to 12 of the National Curriculum. The fellow student should understand the number system and related operations. There are some relationships exist in between number systems of various types. We often come across four different number systems in computer Science. For the class works and mathematical operations of School Education we restrict our discussion to decimal system only. I hope the kind of effort and combination of problems might enhance the knowledge base of our fellow students. For Parents Questions are there without respective answers. It can be obtained from the source. There exists a plan of fulfilling dual purpose of the effort. These sets can be utilized to engage a student for working out the possible outputs without being inflicted primarily with answers. If answers are provided alongside the questions then the material will fulfill half of the purpose. It cannot contingent for overcoming the problems and also cannot facilitate in skill enhancement efforts. Set of questions can be used for the purpose of assessing skill acquisition process and also can be assigned to the ward by parents and guides. It is not mandatory to go through all sets of problems, but not to skip any of the problems is recommended for assuring the perfect skill acquisition. vii

Fundamentals

This workbook cannot cover any theoretical perspective related to the organic compounds. All the questions and model answers are incorporated in this volume from previously conducted board exams and other competitive exams. Most of the questions carry model answers. Some of the questions left un- attended because of their similarity with other identical questions. One can explore all such questions and relevant answers for gaining adequate skills in addressing the subject. All the topics from High School Science are considered with an approach of the convergence of curriculum for making the content area of this workbook a compact one. In some cases similar questions may appear for two to three times due to their chances of repeated accommodation in the previous year question papers of various schools of studies.

Chandan Sengupta

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Fundamentals Organic Chemistry is the field of studies that deals with the chemicals having some organic sources. Chemicals containing carbon as one of the constituents are incorporated in the studies of organic chemistry. We obtain different types of organic compounds from both natural and synthetic sources. Majority of hydrocarbons are naturally obtained from petroleum and associated fossil fuels. We can even prepare some other chemicals in laboratory. Structural representation and empirical formula of any organic compound starts with C, and is followed by H atom. This indicates the obligatory presence of carbon and hydrogen in any organic compound. Structural formulae of any organic compound are represented in a condensed pattern. This pattern is useful for representing large molecules. Another way of representing these compounds is by displaying bonds only, with an understanding that carbons and hydrogen present in the chain are never explicitly displayed.

H H H H

C–C–C

H

CH3CH2CH3

H H H Representation of Propane in three different ways

All these three representations display the structural particulars of propane. We can even efficiently display isomers of organic compounds with easiness through bond line structure.

Try to draw line structure of the following: 1. octane[ ]

7. 2,3-dimethylhexane

2. 2-methylheptane

8. 2,4-dimethylhexane

3. 3-methylheptane

9. 2,5-dimethylhexane

4. 4-methylheptane

10. 3,4-dimethylhexane

5. 2,2-dimethylhexane

11. 3-ethylhexane

6. 3,3-dimethylhexane

12. 2,2,3-trimethylpentane

Fundamentals

13. 2,2,4-trimethylpentane

16. 3-ethyl-2-methylpentane

14. 2,3,3-trimethylpentane

17. 3-ethyl-3-methylpentane

15. 2,3,4-trimethylpentane

18. 2,2,3,3-tetramethylbutane

Alcohols exhibit condensation reaction and form ester. During this reaction water is casted off from the alcohol molecule to make the formation of higher alcohols possible. Example:

CH3CH2OH + CH3CH2OH = CH3CH2CH2CH2OH + H2O

[Ethanol condenses to form butanol. one molecule of water is liberated during this process. ] Condensation of alcohol and carboxylic acid results in the formation of an ester. Example: CH3COOH

+

CH3CH2OH

Acetic Acid

=

CH3COOCH2CH3

Ethanol

Ethyl ethanoate (ester)

Substitution Level of carbon present in an organic compound is determined by the number of hydrogen atoms attached to that carbon atom. It can be primary (3 hydrogen attachment), secondary (2 H attachment), and tertiary (1 H attachment) or quaternary (0 H attachment) .

Cl

Cl

Cl a.

b.

c.

d.

In case of amines the nomenclature rules are little bit different. There are three different types of amines on the basis of hydrogen attached to nitrogen. It may be primary (2H on N), secondary (1H on N) or tertiary (0 H on N).

We may represent organic compounds in different ways. It may be through structural formula or may be through molecular formula.

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Properties of Carbon Carbon is unique because of some of its properties. If we observe the electron arrangement in carbon atom then we find two different arrangements of electrons. One arrangement will be at the ground state. Another arrangement will be at excited state. Electron congiguration of carbon at ground state is 1s2 2s2 2p2 .

Arrangement of electrons in carbon atom: Electron arrangement Ground State

1s

2s

2px

2py

2pz

2py

2pz

Electron arrangement Excited State

1s

2s

2px

This arrangement of electrons ensures the valency of carbon as four. All the four valence electrons attain the identical status in terms of the levels of energy. Two energy levels of the second shell fuse to form a single energy level to all the four valence electrons. This hybridization is accomplished through interactions of 2s, 2px, 2py and 2pz orbitals making it a hybridization pattern titled sp3 hybridization. Overlapping of s-s, s-p and p-p orbitals result in the formation of strong sigma bond. End to end overlap of atomic orbitals along the internuclear axis results in the formation of such a strong bond. It also ensures a definite tetrahedral structure of the carbon atom. We can go through the structure of a methane molecule to understand this tetrahedral structure of the carbon atom. All the C-H bonds present in methane are identical. All the bonds do not lie in the same plane. H – C – H bond angle in a methane molecule is found to be 1090 28’. All the four bonds repel each other and remain at the four corners of a regular tetrahedron. xi

Properties of Carbon

It is the normal pattern through which all the saturate hydrocarbons are formed. This unique arrangement of valence electrons in the carbon atom has enabled it to form C - C nested bonds in various open chain patterns having branching and sub branching of various types.

In unsaturated hydrocarbons the formation of sp2 hybridization (alkenes) and sp hybridization takes place. Three sp2 hybridization orbitals repel each other uniformly. Because of this reason they are directed towards three corners of an equilateral triangle. In this type of hybridized orbital pattern one of the lobes is smaller than the other.

Allotropy Allotropy, in the field of chemistry, is a behavior exhibited by certain chemical elements. These elements, commonly identified as allotropes of parent element, can exist in two or more different forms. In each different allotrope, the element's atoms are bonded together in a different manner. Allotropes are different structural modifications of an element. Carbon is such an element having exhibits of allotropy. Some of the popular allotropes of carbon are as follows: a) diamond; b) graphite; c) lonsdaleite; d-f) buckyballs (C60, C540, C70); g) amorphous carbon; h) carbon nanotube.

Bonding Mechanism . In bonds between atoms of the same element the sharing of the electrons is equal between the two atoms. This is referred to as a non-polar covalent bond. The unequal sharing of electrons is called a polar covalent bond. This kind of unequal sharing of electron is observed in case of bonding between carbon and other atoms, such as C-H, C-Cl, C-F etc. The definition of a polar covalent bond is a covalent bond in which the bonding electrons spend more time near one atom than the other. VSEPR (valence-shell electron pair repulsion) theory states that valence pairs (pairs available for bonding) are arranged as far from each other as possible. The repulsion force between electrons is

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what gives rise to the shape of molecules. Notice in the above structure of methane that the hydrogen o atoms are located as far apart as possible, giving angles of 109.5 between them.

Primary, Secondary and Tertiary Carbon A primary carbon (1º) is one that is bonded to no more than a single carbon atom. Such kind of a pair of primary carbon can be located in the molecules of ethane, ethanol, ethanoic acid, CH3CHO and some other derivatives. C2H5-O-C2H5 is also having primary carbons. A secondary carbon (2º) is bonded to two other carbon atoms. Carbon atoms of secondary type can be located in hydrcarbons having more than two carbon atoms, such as propane, butane etc. The tertiary (3º) and quaternary (4º) carbon atoms are bonded respectively to three and four other carbons. The three C6H14 isomers , such as 3-methylpentane, 2,3 –di methylbutane, 2,2 – dimethylbutane and n-Hexane, shown below illustrate the location of secondary, tertiary and quaternary carbon atoms.

Primary Carbon Tertiary Carbon

Quaternary Carbon

Secondary Carbon

There are several such instances in which we can locate all the four types of carbon atoms as categorised and displayed above.

Bonding in Carbon: The Covalent bond, Electron dot structure, Physical properties of organic compounds, Allotropes of Carbon. Covalent Bond: The atomic number of carbon is 6. Its electronic configuration is 2, 4. It requires, 4 electrons to achieve the inert gas electronic configuration. But carbon cannot form an ionic bond

Properties of Carbon

It could gain four electrons forming C4- cation. But it would be difficult for the nucleus with six protons to hold on to ten electrons. It could lose four electrons forming C4+ cations. But it requires a large amount of energy to remove four electrons. Thus, carbon overcomes this problem by sharing of its valence electrons with other carbon atoms or with atoms of other elements. The bond formed by mutual sharing of electron pairs between two atoms in a molecule is known as Covalent Bond. Types of Covalent Bond:   

Single Covalent Bond: When a single pair of electrons are shared between two atoms in a molecule. For example; F2, Cl2, H2 etc. Double Covalent Bond: When two pairs of electrons are shared between two atoms in a molecule. For example; O2, CO2 etc. Triple Covalent Bond: When three pairs of electrons are shared between two atoms in a molecule. For example; N2 etc.

Electron Dot Structure: The electron dot structures provide a picture of bonding in molecules in terms of the shared pairs of electrons and octet rule. Formation of Hydrogen Molecule Atomic number of Hydrogen = 1 Number of valence electrons = 1

Formation of CH4 Molecule Atomic number of Carbon = 6 [2, 4] Number of valence electrons = 4 Atomic number of Hydrogen = 1

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Number of valence electrons = 1

Formation of CO2 Molecule Atomic number of Carbon = 6 [2, 4] Number of valence electrons = 4 Atomic number of Oxygen = 8 [2, 6] Number of valence electrons = 6

Formation of H2S Molecule Atomic number of Sulphur = 16 [2, 8, 6] Number of valence electrons = 6

Physical Properties of Organic Compounds Most of the organic compounds have low boiling and melting point, due to the weak force of attraction (i.e., the inter-molecular force of attraction) between these molecules. Most carbon compounds are poor conductors of electricity, due to the absence of free electrons and free ions. Compounds

M.P. (K)

B.P. (K)

Acetic acid (CH3COOH)

290

391

Chloroform (CHCl3)

209

334

Ethanol (CH3CH2OH)

156

351

Methane (CH4)

90

111