XII Organic Chemistry Test Questions on Chapter # 6, Introduction to Organic Chemistry Test # 1

 

Test Questions on Chapter # 6, Introduction to Organic Chemistry Test # 1

 

Q1.   Define the following with examples:

homologous series, functional group, catenation, Polymerization (polymers), isomerism (isomers), metamersim, knocking, octane number, reforming, knock-inhibitor, carbonization, heterocylics.

 

Q2.   Write down differences between following with examples and give one chemical tests to identify them:

(i)           Aliphatic and aromatic compounds (Soot Test)              

(ii)         Saturated and unsaturated compounds (BUT)

 

Q3.  Write down Condensed general formulae of following homologous series:

Alkenes (CnH2n), 

Aldehydes (CnH2nO), 

Carboxylic acids (CnH2nO2), 

Alkynes (CnH2n-2), 

Esters (CnH2nO2),                 

Ketones (CnH2nO), 

cylcoalkanes (CnH2n), 

cycloalkenes (CnH2n-2).

 

Q4. Name the alkanes, alkenes and alkynes having the following formula

(i) C2H4 (ethene)             

(ii) C3H4 (propyne)        

(iii) C2H6 (ethane)          

(iv) C6H12 (hexene or cylcohexane)

(v) C5H8 (pentyne)         

(vi) C8H16 (Octene)        

(vii) C7H12 (Heptane)    

(viii) C6H10 (Hexyne)


Q5. Identify the series with following general formulae:






Q6.  


Q6. What are alkyl groups? Give its general formula and type formula. Describe name and structural formulae of butyl and pentyl radical.

 

Q7. What is meant by homologous series? Describe 4 general features of homologous series

 

Q8. Write down short note on any 5 carbon-containing and 5 oxygen-containing functional groups.

 

Q9.Write down names and draw structural formulae three positional isomers of cresol.

 

Q10. Write down names and draw structural formulae three positional isomers of xylenes

 

Q11. What is the functional group of ethers? Give their general formula. Write down their classification with examples.

 

Q12. What is the functional group of ketones? Give their general formula. Write down their classification with examples.

 

Q13.Write general formula for aldehydes and carboxylic acids. Name and give formulae of first six members of aldehydes and carboxylic acids.

 

Q14. Identify the functional groups in the following compounds:

(a) CH3CHO (Aldehydic group)                                

(b) CH3CH2CH2OH (primary alcoholic group

(c) CH3COCH3 (ketonic carbonyl group)              

(d) CH3COOH (carboxylic group)           

(e) CH2=CHCH3 (double bond)                                  

(f) CH3CONH2 (Amide group)

 

Q15. Write down formulae and class of following functional groups:

Epoxide group, Carbonyl group, Olefinic double bond, Ether linkage, Sulphonic acid group, Nitrile group 

 

Q16.Encircle the functional groups in the following compounds. Also give the names of the functional groups?




Q17.      Give structural formulae of following compounds:

(1)     Picric acid      

(2)     Pyrogallol               

 (3)     Catechol   

 (4)     Resorcinol                  

(5)     b-naphthol  

(6)     Hydroquinone  

(7)     Terephthalic acid                        

(8)     trifluoro acetic acid       

(9)     diphenyl amine    

(10)   α-naphthol            

(11)       isopropyl methanoate 

(12)       iso-butyric acid      

(13)       diethyl acetylene 

(14)       divinyl acetylene              

(15)       1,4-hexadiene                                   

(16)       tribromoethanal                      

(17)       4, 5-dimethyl 3-heptanone         

(18)       Methyl isopropyl ether        

(19)       Ethyl ethanoate 

 (20)       3-ethoxyhexane    

(21)     Ethyl ter-butyl ether        

(22)     Glyoxal                         

(23)     isobutyraldehyde  

(24)     p-cresol

(25)     Valeric acid

(26)     diisopropyl ether

(27)     Neopentyl alcohol

(28)     Pyrogallol

(29)     Caproic acid

(30)     Phenylhydrazine   

            

                      


Answers of Test Questions on Chapter # 6, Introduction to Organic Chemistry Test # 1

 

Q1.   Define the following with examples:

Alkyl group, homologous series, functional group, catenation, Polymerization (polymers), isomerism (isomers), metamersim, knocking, octane number, reforming, knock-inhibitor, carbonization, heterocylics.

Answer

Catenation (a unique property of carbon)

The property of carbon atoms to bond or link itself to other carbon atoms forming long chains, branched chains, rings or compounds with chains and rings together is called Catenation.

 

Alkyl Radicals                                                                               

Alkyl groups are the basic structural unit of all aliphatic organic compounds. The residual hydrocarbon group or radical left after the removal of a hydrogen atom from a saturated hydrocarbon alkane is called an alkyl group or radical.

 

Homologous Series

The members of the same class of organic compounds arranged in order of ascending molecular masses having same functional group whose successive members differ from each other by an integral number of methylene groups (–CH2–) in their molecular formulae (or by molecular mass of 14) are said to form a Homologous Series.

 

Functional Group

An atom or group of atoms which is present within the organic molecule and is responsible for its chemical behaviour and characteristic properties is called Functional Group.

 

Polymerization (polymers)

It is a chemical reaction in which a large number of smaller molecules called monomers react together to form a larger molecule called polymer that contains repeating structural units. The macromolecules               formed may have a linear or branched structure with complex three-dimensional network.

 

isomerism (isomers)

Isomerism is the existence of different compounds exhibiting different physical or chemical properties or both having same molecular formula i.e. The phenomenon of existence of two or more compounds possessing the same molecular formula but different properties is known as isomerism. Such compounds are called as isomers.

 

metamersim

Isomerism resulting from unequal distribution of carbon atoms (alkyl or aryl groups) on either side of the polyvalent functional group is called metamerism.

Different compounds which have same molecular formula having same functional group in which polyvalent atom of the same functional group joins different combinations of alkyl or aryl radicals are called metamers. 

 

knocking

A sharp metallic sound or tapping noise produced in the internal combustion engine due to pre-ignition or premature combustion of the fuel in the cylinder prior to sparking is called Knocking or Pinking.

 

octane number

it is the capacity of a sample of gasoline to resist knocking expressed as a number equal to the percentage of isooctane in an isooctane-heptane mixture that has the same knocking characteristics.

 

reforming

The process in which the atoms are rearranged in straight chain alkanes (obtained from gasoline fractions) to produce branched chain alkanes or aromatic hydrocarbons is known as Reforming or Isomerisation. It is the conversion of straight hydrocarbon into branched chain hydrocarbons in order to increase the octane number of a fuel to avoid knocking.

 

knock-inhibitor

The knock inhibitors or anti-knocking agent (acting as Catalysts) like tetraethyl Lead, TEL [(C2H5)4Pb) greatly reduce knocking by enhancing octane number of fuel. 

 

carbonization

Thermal decomposition of a highly carbonaceous material such as coal in the absence of air resulting in decomposition to solids, liquids and gases is called Carbonization or Destructive Distillation.

 

heterocylics

The cyclic compounds having one or more hetero atoms (like nitrogen, sulphur or oxygen) along with carbon in the ring are called Heterocyclic or Non-Carbocyclic Compounds e.g. Pyrole/Ozole, Furan/Oxole, Thiophene/thiole, Pyridine/Azine

 

 Q2.Write down difference between following with examples and give two chemical tests to identify them:

 (i) Aliphatic and aromatic compounds (Soot Test)

 (ii) Saturated and unsaturated compounds (BUT)

Answer

 

Difference between Aliphatic and Aromatic Compounds

 



Difference between Aliphatic and Aromatic Compounds




Difference between Saturated and Unsaturated Hydrocarbons





Q3. Write down Condensed general formulae of following homologous series:

Answer

Alkenes …………………..   CnH2n)

Aldehydes……………….   (CnH2nO)

Carboxylic acids ……..    (CnH2nO2)

Alkynes …………………     (CnH2n-2)

Esters …………………..      (CnH2nO2)           

Ketones ………………..      (CnH2nO)

Cylcoalkanes…………      (CnH2n)

Cycloalkenes…………      (CnH2n-2).

 

Q4. Name the alkanes, alkenes and alkynes having the following formula

Answer

(i) C2H4 (ethene)            

(ii) C3H4 (propyne)       

(iii) C2H6 (ethane)         

(iv) C6H12 (hexene or cylcohexane)

(v) C5H8 (pentyne)        

(vi) C8H16 (Octene)       

(vii) C7H12 (Heptane)   

(viii) C6H10 (Hexyne)

 

Q5.  Identify the series with following general formulae:

Answer

 

CnH2n                               [n = 2 to infinity]………………....   Alkene  

CnH2nO2                        [n = 1 to infinity]…………………   Acids      

CnH2n+2O                     [n = 2 to infinity]…………….. ...    Alkane  

CnH2nO                   [n = 3 to infinity]…………………. Ketones or oxirane         

CnH2n+1CONH2    [n = 1 to infinity]…………………. Acid amide          

CnH2nO2                        [n = 2 to infinity]…………………   Ester

CnH2n+1CONH2    [n = 1 to infinity]…………………   Acid amide

CnH2n+2O                     [n = 1 to infinity]………………….  Alcohols

CnH2n                               [n = 2 to infinity]………………….  Alkene

CnH2nO2                        [n = 1 to infinity]…………………   Aldehydes

 

Q6.  What are alkyl groups? Give its general formula and type formula. Describe name and structural formulae of butyl and pentyl radical.

Answer

Definition of Alkyl Radicals                                                                     

Alkyl groups are the basic structural unit of all aliphatic organic compounds.

 

The residual hydrocarbon group or radical left after the removal of a hydrogen atom from a saturated hydrocarbon alkane is called an alkyl group or radical. Stated differently, the radicals obtained from alkanes by the removal of one hydrogen atom are called alkyl group or radical. The smallest alkyl group is CH3 called methyl.

 




Alkyl radicals are derivatives of alkanes. Alkanes are quite often represented as R-H and here R stands for alkyl group. Alkyl groups are generally represented by ‘R–‘. 


Butyl Group; (C4H9–); It may exist in 4 isomeric forms:

It is derived from butane (C4H10) having formula C4H9.It may exist in 4 isomeric forms.



(v)      Pentyl Group or Amyl group (C5H11–); It may exist in 8 isomeric forms:     

Pentyl group (C5H11–) has the following 8 isomers, 4 are primary, 3 are secondary and 1 is tertiary:



Q7. What is meant by homologous series? Describe 4 general features of homologous series

Answer

Definition

“The members of the same class of organic compounds arranged in order of ascending molecular masses having same functional group whose successive members differ from each other by an integral number of methylene groups (–CH2–) in their molecular formulae (or by molecular mass of 14) are said to form a Homologous Series.”

 

For example; In the first ten members of alkanes (C1 – C10), each member differs from its neighbour by –CH2– group. There is a gradual change in their physical properties with increasing molecular weight but chemical properties like combustion, halogenation are same.

 

e.g.

General characteristics of homologous series

 

1. Identical structures and common difference in composition

All members of a homologous series have identical structures. Successive members of a series always differ in composition by an integral number of methylene groups (–CH2–). The difference between the molecular weights of two successive members of a series will be of 14 amu (u). The name of each member of a series begins either with a common prefix or suffix.

 

2. General Molecular Formula

All members of a homologous series can be expressed by a general molecular formula. For example:






3. General Method of Preparation

All members of a homologous series can be prepared by a common general method of preparation

e.g.

all members of alkanes can be prepared by reduction of alkyl halide by nascent hydrogen [H]:




4. Identical Chemical Properties

The elements and functional group present in compound of a homologous series are same. Homologues show almost identical chemical properties due to the presence of identical functional group.

e.g.

all alkanes are unreactive under ordinary conditions. They undergo combustion and substitution reaction with halogens.

 


Q8. Write down short note on any 5 carbon-containing and 5 oxygen-containing functional groups.

Answer

 

1. Ketones; (>C=O)

It is the series of organic compounds in which carbonyl group is directly linked to two carbon atoms of alkyl radicals. e.g.

 

(i) H3C–CO–CH3 (Acetone or Propanone)                                                        

(ii) C2H5–CO–CH3 (2-butanone)                                                                            











2.   Aldehydes; (–CHO)

It is the series of organic compounds in which carbonyl group is directly linked to at least one hydrogen atom (except formaldehyde). 






e.g.




                                                      O

                                                      ||

3.            Carboxyl Group ( –C–OH   or   –COOH)

It is the combination of a carbonyl group and a hydroxyl group i.e. –CO–OH  or  –COOH. Carboxyl group is the functional group of carboxylic acids. 









e.g.

 









Following are the derivatives functional groups of carboxyl groups:

(a)          Acid Halides (–CO–X)

(b)         Acid Amides (–CONH2)

(c)          Ester Group       (–COO–R)

(d)         Acid anhydride (–CO O – CO –)

(e)          Nitrile group     (–CN or –CºN)

(f)          Isonitrile group (–NC or – N+ º C-)

                               

(a).   Acid Halides/Halocarbonyl/oylhalide (–CO–X)

The replacement of hydroxyl group from a carboxyl group by a halogen atom gives an acid halide group. It is the functional group of acid halides/Alkanoyl Chloride.

e.g.

 

(i)   H–CO–Cl …………… Formyl chloride (Methanoyl Chloride) 

(ii)   H3C–CO–Cl ………   Acetyl chloride  (Ethanoyl Chloride)

(iii)  C2H5–CO–Cl …… Propionyl chloride (Propanoyl Chloride)

 

(b).   Acid Amides or Amide (–CONH2)

The replacement of hydroxyl group from a carboxyl group by an amino group gives an amide group. It is the functional group of alkanamide family.

e.g.

(i)           H–CO–NH2 ………….. Formamide/Methanamide

(ii)         CH3–CO–NH2 ………. Acetamide/Ethanamide

                                                                               

(i)   Primary amides   ; (–CONH2) (R–CONH2) ; 

e.g.     CH3–CONH2  ,              CH3–CH2–CONH2

(ii)  Secondary amines ; (>CONH) (R–CONH–R)   ;

 e.g.     (CH3)2.CONH

(iii)        Tertiary amine   ; (àCON) (R–CONR2)       ; 

e.g.     CH3–CON.(CH3)2


Like amines, the amides are classified as primary, secondary and tertiary based on the number of carbons connected to the nitrogen.


(c).            Ester Group (–COO–R)

The replacement of hydrogen of hydroxyl group from a carboxyl group by an alkyl group (–R) gives an ester group.  It is the functional group of esters.

e.g.

(i)   H–COO–CH3      …………. Methyl formate (methyl methanoate)

(ii)  CH3–COO–CH3  ………….. Methyl acetate (methyl ethanoate)

(iii) CH3–COO–C2H5 ………….. Ethyl acetate (ethyl ethanoate)

 

(d).  Carboxylic acid anhydride/Acid anhydride group; 

(–CO– O – CO –)  

It is the functional group of acid anhydride family.

 e.g. 

(i)           H–CO–O–CO –H ……………. Formic Anhydride 

(ii)         CH3–CO–O–CO–CH3 …………… Acetic Anhydride 


(e).  Cyanide or Nitrile group (–CN or –CºN)

It is the functional group of alkanenitrile family.

e.g.                                        

(i)           CH3–CN ……………. ethanenitrile

(ii)         C2H5–CN …………… propanenitrile

 

(f).  Isocyanide or Isonitrile or Carbylamine (–NC or – N+ º C-)

It is the functional group of alkaneisonitrile family.

e.g.                        

(i)        CH3–NC …………….. ethaneisonitrile

(ii)       C2H5–NC …………… propaneisonitrile


 

Q9. Write down names and draw structural formulae three positional isomers of cresol.

Answer

Cresol (methylphenol) has three positional isomers which show different physical properties. 





Q10. Write down names and draw structural formulae three positional isomers of xylenes.

Answer

Di-substituted benzenes (DSB) have three positional isomers namely ortho, meta and para e.g. xylene (a DSB) has three positional isomers.





Q11. What is the functional group of ethers? Give their general formula. Write down their classification with examples.

Answer

Ether Linkage

The linkage of two carbon atoms through an oxygen atom is called an Ether linkage (C – O – C). It is the functional group of ether family. 








e.g.

(i)          CH3–O–CH3 …………………. (dimethyl ether)                

(ii)         C2H5–O–CH3 ……………….. (ethyl methyl ether)         

(iii)        C2H5–O–C2H5 ……………… (diethyl ether)                      



Q12. What is the functional group of ketones? Give their general formula. Write down their classification with examples.

Answer

(a) Ketones;    (>C=O)

It is the series of organic compounds in which carbonyl group is directly linked to two carbon atoms of alkyl radicals. e.g.

(i)   H3C–CO–CH3 …………. (Acetone or Propanone)                              

(ii) C2H5–CO–CH3 …..……. (2-butanone)                                                     


Q13.Write general formula for aldehydes and carboxylic acids. Name and give formulae of first six members of aldehydes and carboxylic acids.

Answer

General formula of Aldehydes

CnH2n+1– CHO/ CnH2nO (isomeric with ketone/oxirane/alkenal etc.)

 

First Six Members of Aldehydes

Formaldehyde…………………….. (H – CHO)

Acetaldehyde……………………… (H3C– CHO)

Propionaldehyde…………………(C2H5– CHO)

Butyraldehyde……………………..(C3H7– CHO)

Valeraldehyde……………………… (C4H9– CHO)

Caproaldehyde……………………..(C5H11– CHO)

 

General formula of Carboxylic Acids

CnH2n+1– –COOH / CnH2nO2 (isomeric with ester)

 

First Six Members of Carboxylic Acids

Formic acid                                       (H – COOH)

Acetic acid                                         (H3C– COOH)

Propionic acid                                 (C2H5– COOH)

Butyric acid                                      (C3H7– COOH)

Valeric acid                                       (C4H9– COOH)

Caproic acid                                      (C5H11– COOH)

 

 

Q16. Encircle the functional groups in the following compounds. Also give the names of the functional groups?

Answer

     


                                                                                                                           






Q17.      Give structural formulae of following compounds:















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