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SHORT QUESTIONS

Q.1.     Name three important sources of organic compounds?

Ans.     (i)         Petroleum        (ii)        Coal                             (iii) natural gas

Q.2.     What happens when coal is heated in the absence of air?

Ans.     When coal is heated in the absence of air (from 500 – 1000oC), it is converted into coke, coal gas and coal tar.

Q.3.     What is meant by natural gas?

Ans.     Natural gas is a mixture of low boiling hydrocarbons. Major portion of the natural gas is methane.

Q.4.     What is meant by petroleum?

Ans.     Mineral oil when it is in the refined form is called petroleum. Petroleum is naturally occurring brown greenish black viscous oily liquid which is obtained from earth’s crust.

Q.5.     Define isomerism with examples.

a)         Two or more compounds which have the same molecular formula but different structural formulas are called isomers and the phenomenon is called isomerism. The number of possible isomers increase as the number of carbon in a hydrocarbon (or organic compound) increases. For example, Butane, C4H10 has two structural isomers, pentane, C5H12 has three isomers and hexane, C6H14 has five isomers.

Q.6.     What is meant by thermal cracking?

Ans.     Breaking down of large molecules by heating at high temperature and pressure is called thermal cracking. It is useful in the production of unsaturated  hydrocarbons such as ethene and propene.

Q.7.     What is meant by catalytic cracking?

Ans.     Breaking down of higher hydrocarbons at lower temperature (500oC) and lower pressure (2 atm) in the presence of a suitable catalyst like SiO2 and Al2O3, is called catalytic cracking. This method is used to get better quality gasoline.

Q.8.     What is meant by steam cracking?

Ans.     The process in which hydrocarbons in the vapour phase are mixed with steam, heated for a short duration to about 900oC and cooled rapidly, is called steam cracking. The process is suitable for obtaining lower unsaturated hydrocarbons.

Q.9.     What is reforming?

Ans.     The process of conversion of straight-chain alkanes (from Gasoline ) into branched-chain alkanes by heating in the presence of Alcl3 catalyst is called reforming. Normal alkanes detonate and cause knocking of the engine, and are bad fuels, while branched-chain alkanes are excellent fuels. The quality of a fuel is indicated by its octane number. The higher the octane number, the lower the knocking tendency. The octane number of gasoline may be increased by reforming.

Q.10.   what are acyclic compounds?

Ans.     Compounds which contain an open chain of carbon atoms are called aliphatic or acyclic compounds. These may be branched or straight chain

                                                      

Q.11.   Give one important use of Gasoline.

Ans.     Gasoline is used as fuel for Vehicles.

Q.12.   What are heterocyclic compounds? Give two examples.

Ans.     Cyclic compounds in which the ring is made up of more than one kind of atoms are called heterocyclic compounds or heterocycles.

The examples are:

Q.13.   Define carbocyclic compounds?

Ans.     The cyclic compounds which have rings made of only carbon atoms are called hemicyclic compounds have been further classified into two classes:

  • Alicyclic compounds                   
  • Aromatic compounds.

Q.14.   What are alicyclic compounds?

Ans.     Carbocyclic compounds which do not have benzene ring and resemble with acyclic compounds in properties are called alicyclic compounds.

Q.15.   What are aromatic compounds?

Ans.     Carbocyclic compounds which contain at least one benzene ring in their molecules are called aromatic compounds.

Q.16.   Define cyclic compounds.

Ans.     Compounds which contain closed chain of atoms are called cyclic compounds. These are of two types:

  1.   Carbocyclic compounds                            (2)        heterocyclic compounds

Q.17.   Define a functional group

Ans.     An atom or group of atoms or a double bond or a triple bond which imparts characteristic properties to organic compounds is called a functional group.

Q.18.   What is the functional group of alcohol?

Ans.     The functional group of alcohols is –OH, called hydroxyl group.

Q.19.   What is the functional group of aldehyde?

Ans.     The functional group of aldehydes is –CHO (   C =    O ) called formyl group.

Q.20.   What is the functional group of ketones?

Ans.     Carbonyl group,           C = O

Q.21.   What is the functional group of carboxylic acid?                                                                                                                                                                 

Ans.     Carboxylic group,  – C – OH

Q.22.   What is sp3 hybridization?

Ans.     The process of mixing s and three P atomic orbitals to form four new equivalent hybrid orbital is called sp3 hybridization. These four sp3 hybrid orbitals are degenerate and are directed at an angle of 109.28o in space to give a tetrahedral geometry. Sp3 hybridization occurs when carbon atomic bonded with four other atoms like hydrogen.

Q.23.   What is sp2 hybridization?

Ans.     The process of mixing together one 2s and two 2p orbitals of carbon to form three equivalent and coplanar sp2 hybridizing orbitals is called sp2 hybridization. Each sp2 hybrid orbital is directly from the center of an equilateral triangle to its three corners making an angle 120o between any two sp3 hybrid orbitals. The unhybridised p-orbital of each carbon will then overlap in a parallel fashion to form a  bond.

Q.24.   What is sp hybridization?

Ans.     The process by which one 2s and one 2p orbitals of the carbon atom mix together to form two degenerate sp hybrid orbitals is called sp hybridization. These hybrid  orbitals have linear shape with a bond angle 180o. the two unhybridised atomic orbitals 2py and 2pz are perpendicular to these sp hybridized orbitals. In alkynes (ethyne), the two unhybridised p orbitals on a carbon atom will overlap separately with the unhybridised p orbitals of the other carbon atom to give two  bonds both perpendicular to the frame work of ethyne.

Q.25.   What is geometrical isomerism?

Such compounds which have the same structural formula but differ with respect to the positions of the identical group in space are called cis-trans or geometric isomerism.

Q.26.   What is meant by cis-isomer and trans-isomer?

Ans.     The cis isomer is one in which two similar groups are on the same side of the of the double bond. The trans isomer is that in which two similar groups are on the opposite sides of the double bond.

Q.27.   What is the necessary and sufficient condition for a compound to exhibit geometric  isomerism?

Ans.     The necessary and sufficient condition for a compound to exhibit geometric isomerism is that the two groups attached to the same carbon must be different.

Q.28.   What is an oil refinery? Mention oil refineries in Pakistan?

Ans.     The industry which purify petroleum and separate different components of petroleum is called oil refinery. In Pakistan we have Attock oil refinery located at Morgah near Rawalpindi, Pak Arab refinery located at Mahmud  Kot near Multan and two oil refineries at Karachi.

Q.29.   What is meant by knocking of petroleum?

Ans.     Knocking is a sharp metallic sound which is produced during the combustion of gasoline in a automobile engine. Knocking reduces the efficiency of an engine.

Q.30.   What is meant by octane number?

Ans.     The octane number of a particularoline is that percent of 2,2,4-trimethyl pentane in a mixture of 2,24-trimethyl pentane and n-haptane which gives equivalent knock performance. 2,2,4-trimethyl pentane burns very smoothly in an engine and has octane number of 100.

Q.31.   What is meant by a homologous series?

Ans.     A homolgous series is a series of compounds in which adjacent members differ by a CH2 unit. The individual members are called homologs. For example, the homolgous series of alkane is: CH4, C2H6,C3H8,C4H10,C5H12,CH4 is homolog of C2H6.

Q.32.   Draw the structure of CH4 and CCl4 indicating the hybridization of central atom?

Ans.     The central atom carbon both in CH4 and CCl4 is sp3 hybridized. In CH4, each C-H CCl4 each C – Cl bond, results from sp3 –s overlap.

Q.33.   Draw the structures of ethene and ethyne

Ans.    

Q.34.   What are two types of homocyclic compounds?

Ans.     The two types of homocyclic compounds are (i) Alicyclic and           (ii)        Aromatic compounds.

Q.35.   Name the two types of cyclic compounds?

Ans.     1.         Carbocyclic compounds                      2.         Heterocylic compounds

Q.36.   Define functional group isomerism with examples,

Ans.     Compounds having the same molecular formula but different functional groups are called functional group isomers and the phenomenon is called functional group isomerism. For example, ethyl alcohol and dimethyl exhibit functional group isomerism.

            CH3CH2OH                                          CH3 –  O – CH3

            Ethyl alcohol                                       Dimethyl ether

Q.37.   Define position isomerism with examples.

Ans.     Compounds which have the same carbon chains but differ in the relative position of the same functional group are called positional isomers and the phenomenon is called position isomerism. Chloropropene has two positional isomers.                         

C3H – CH2 – CH = CH2                       H3C – CH = CH – CH3 (isomers of Butene)

            1-Butene                                  2-Butene

Q.38.   What is Metamerism? Give examples.

Ans.     Metamerism is a type of structural isomerism in which alkyl groups are different on both sides of functional group. Metamers are the same family of compounds and is mostly given by ethers, ketones, amines and esters.

CH3CH2 – O – CH2CH3 and CH3OCH2CH2CH3 are metamers

Diethyl ketone                         Methyl n-proply ether

Q.39.   Organic compounds generally give slow reactions as compared to inorganic compounds. Why?

Ans.     Organic compounds are generally covalent in nature and insoluble in water. Their polarity is not so much pronounced. Thus, organic compounds give show reactions.

Q.40.   What is vital force theory?

Ans.     The early chemists considered that organic compounds were synthesized only by and within living things, plants or animals and these compounds could never be synthesized from inorganic materials. This concept was referred to as vital force theory.

Q.41.   Which organic compounds was first of all prepared in the laboratory.

Ans.     Friedrick Wohler prepared urea by heating ammonium cyanate in the laboratory. Urea is also present in the urine of mammals.

NH4CHO  (NH2)2CO

Q.42.   What is modern definition of organic chemistry?
ans.      The branch of chemistry which deals with the study of compounds of carbon and hydrogen (hydrocarbons) and their derivatives is called organic chemistry.

Q.43.   What is knocking of engine?

Ans.     A sharp metallic sound produced in the internal combustion engine which is due to gasoline of low octane number is called knocking of engine.

Q.44.   How do you define octane number and how it can be improved?

Ans.     The octane number of a particular gasoline is that percent of 2,2,4-trimethylpentane in a mixture of 2,2,4-trimethylpentane and n-heptane which give equivalent knock performance. 2,24-trimethylpentane, with no tendency to knock is assigned the octane number of gasoline is improved by a process called reforming. It involves the conversion of straight chain hydrocarbons into branched chain by heat in the absence of oxygen and in the presence of a catalyst.

Q.46.   Give four examples of compounds heterocyclic?

Ans.     The following are the example of heterocyclic compounds.

Q.47.   1-butene does not show geometrical isomerism but

            2-butene exhibits geometrical isomerism. Why?

Ans.     The necessary condition for a compound to exhibit geometric isomerism is that the two atoms or group bonded to the same double – donned carbon must be different. In 1-butene two similar hydrogen atoms are present at a double-bonded carbon so it does not exhibit geometrical isomerism. But in 2-butene two different groups are bonded to the double-bonded carbon, so it exhibits geometrical isomerism.                                 

Q.48.   Butyne does not show geometrical isomerism, but 2-butene does. Why?

Ans.     Geometrical isomerism results from a restriction in rotation about double bonds but in 2-butyne only one group is attached to the triply-bonded carbons, so it cannot show geometrical isomerism.                              

Q.49.   Why there is no free rotation around a double bond and a free rotation around a single bond.

Ans.     A double bond consists of a  (sigma) and a  (pi) bond. Free rotation around the double bond is not possible because rotation will break the “pi” bond. While a single bond consists of only a sigma bond and it is easy to rotate any thing around a single point, so there is free rotation around a single bond.

Q.50.   Write structural formulas of two possible isomers of C4H10. Also write their IUPAC Names.

Ans.     The two possible isomers of C4H10 are:                                 

12 thoughts on “Fundamental Principles of Organic Chemistry”
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