Alkanes

Question 1

What are the simplest organic compounds made up of only carbon and hydrogen called?

Answer 1

They are known as hydrocarbons.

Question 2

How are hydrocarbons classified?

Answer 2

They are classified into two groups: saturated hydrocarbons and unsaturated hydrocarbons.

Question 3

What are saturated hydrocarbons?

Answer 3

Those in which all four valences of carbon atoms are saturated by single bonds to four hydrogen or carbon atoms.

Question 4

What are unsaturated hydrocarbons?

Answer 4

The type in which carbon atoms are linked together by multiple bonds (at least one double bond or triple bond).

Question 5

What are aliphatic hydrocarbons?

Answer 5

Those having an open chain of carbon atoms.

Question 6

What is the general formula for alkanes?

Answer 6

CₙH₂ₙ₊₂ (where n = number of carbon atoms).

Question 7

What is the structure of alkanes?

Answer 7

A chain of carbon atoms that contains the maximum number of hydrogen atoms.

Question 8

What is the hybridization of carbon atoms in alkanes?

Answer 8

The carbon atom in an alkane has four sp³ hybridized and forms four single bonds.

Question 9

What is the bond length and bond angle in alkanes?

Answer 9

C-C bond length is 1.54 Å and bond angles are 109.5°.

Question 10

What are the main constituents of natural gas and petroleum?

Answer 10

Alkanes.

Question 11

What are the first ten alkanes?

Answer 11

Methane, Ethane, Propane, Butane, Pentane, Hexane, Heptane.

Question 12

What is the significance of the names of alkanes?

Answer 12

The names of alkanes form the basis for the names of many other types of organic compounds.

Question 13

What is the first step in alkane nomenclature?

Answer 13

Identify the longest continuous carbon chain as the parent chain.

Question 14

What to do if there are multiple chains of equal length?

Answer 14

Choose the one with the greater number of branch points (substituents) as the parent.

Question 15

How should carbon atoms of the parent chain be numbered?

Answer 15

Number the carbon atoms so that any branch points have the lowest possible number.

Question 16

What is the process for identifying substituents?

Answer 16

Identify and number the substituents and list them in alphabetical order.

Question 17

What to do if there are two substituents on the same carbon?

Answer 17

Assign them the same number.

Question 18

How should the name of the compound be written?

Answer 18

Write out the name as a single word: hyphens separate prefixes, commas separate numbers.

Question 19

How are identical substituents indicated in nomenclature?

Answer 19

Use prefixes: di- for two, tri- for three, tetra- for four.

Question 20

What is an alkene?

Answer 20

An unsaturated hydrocarbon.

Question 21

What is the general method for laboratory synthesis of alkanes?

Answer 21

Members of a homologous series can be prepared by similar general methods.

Question 22

What is the hydrogenation reaction for alkenes?

Answer 22

RCH=CH + H2 → RCH2CH3.

Question 23

What is the hydrogenation reaction for alkynes?

Answer 23

R-C≡C-R + 2H2 → RCH2CH3.

Question 24

What are examples of alkanes?

Answer 24

Examples include octane, nonane, ethane, and decane.

Question 25

What is the temperature requirement when using nickel as a catalyst?

Answer 25

Higher temperature of 250°C to 300°C is required.

Question 26

What is the reaction known as when using nickel?

Answer 26

The reaction is known as the Sabatier-Senderens reaction.

Question 27

Can methane be prepared through the Wurt reaction?

Answer 27

No, methane cannot be prepared through this method.

Question 28

What are alkyl halides converted to when reduced with zinc and hydrochloric acid?

Answer 28

Alkyl halides are converted to their corresponding alkanes.

Question 29

What is the general reaction for converting alkyl halides to alkanes?

Answer 29

R-X + 2H → RH + HX

Question 30

What is the Wurt reaction?

Answer 30

A process where alkyl halides react with sodium metal in ether solution to produce alkanes.

Question 31

What are the limitations of the Wurt reaction?

Answer 31

Methane cannot be prepared, and the reaction fails in the case of tetra alkyl halides.

Question 32

What is Frankland's method?

Answer 32

Heating alkyl halides with zinc in an inert solvent to form higher alkanes.

Question 33

What does Frankland's method involve?

Answer 33

The formation of an intermediate organozinc compound.

Question 34

How are alkanes formed from carboxylic acid salts?

Answer 34

By heating carboxylic acid salts of sodium with soda lime.

Question 35

What is the reaction for decarboxylation of monocarboxylic acids?

Answer 35

RCOONa + NaOH → RH + NaCO₂

Question 36

What is soda lime?

Answer 36

Soda lime is prepared by soaking quick lime (CaO) with caustic soda solution and drying the product.

Question 37

What are Grignard reagents?

Answer 37

Grignard reagents are alkyl magnesium halides that produce pure alkanes when treated with compounds containing active hydrogen like water, amines, and alcohols.

Question 38

What is the reaction of Grignard reagent with water?

Answer 38

RMgX + HOH → Alkanes ## Footnote Example: C2H5MgBr + HOH → C2H6 + Mg(Br)OH

Question 39

How are alkanes produced using lithium dialkyl copper reagent?

Answer 39

Treatment of lithium dialkyl copper reagent (R2CuLi) produces alkanes.

Question 40

What is Kolbe synthesis?

Answer 40

Kolbe synthesis is the anodic oxidation of carboxylic acids to produce symmetrical alkanes.

Question 41

What is the general reaction for Kolbe synthesis?

Answer 41

2RCOOH → R-R + 2CO2 + 2H + 2e

Question 42

What is the industrial synthesis of ethane?

Answer 42

RH + Mg(x)OH + CH3 + Mg(Br)OH → Ethane

Question 43

What is catalytic alkylation?

Answer 43

Catalytic alkylation of isobutane with hydrogen fluoride as a catalyst provides an economical means for producing high octane motor fuel from refinery gases.

Question 44

What are the physical properties of alkanes?

Answer 44

Alkanes containing up to four carbon atoms are colorless, odorless gases, while others are colorless and odorless liquids or solids.

Question 45

What is the solubility of alkanes in polar solvents?

Answer 45

Alkanes are non-polar molecules and almost insoluble in polar solvents like water, making them hydrophobic.

Question 46

How does branching affect boiling points of alkanes?

Answer 46

Branching decreases the boiling point, adding a CH2 or CH3 group increases the boiling point by 20-30°, and forming a ring increases the boiling point by 10-20°.

Question 47

What is halogenation in alkanes?

Answer 47

Halogenation is the reaction of alkanes with halogen in the presence of UV light or high temperature, resulting in the substitution of hydrogen with halogen.

Question 48

What is nitration in alkanes?

Answer 48

Nitration is the replacement of hydrogen by a nitro (NO₂) group in alkanes.

Question 49

What is the general reaction for nitration?

Answer 49

R-H + HONO₂ → RNO₂ + H₂O

Question 50

What is sulphonation in alkanes?

Answer 50

Sulphonation involves the reaction of alkanes with fuming tetraoxosulphate (VI) acid, yielding sulphonic acid.

Question 51

What is the general reaction for sulphonation?

Answer 51

RH + H₂SO₄ → RSO₃H + H₂SO₄

Question 52

What is thermal decomposition (pyrolysis) in alkanes?

Answer 52

Thermal decomposition, or pyrolysis, involves the breaking down of alkanes at high temperatures.

Question 53

What is a specific example of sulphonation?

Answer 53

(CH₃)₂CH + H₂SO₄ → (CH₃)₂C-SO₃H + H₂SO₄