Chapter 11: Hydrocarbons

(i) Cycloalkanes: Saturated hydrocarbons with carbon atoms arranged in a ring, having the general formula C,H2n. (ii) Isomerism: The phenomenon where compounds have the same molecular formula but different structures or spatial arrangements. (iii) Conjugated dienes: Dienes in which two double bonds are separated by one electron bond, single allowing delocalization (e.g., 1,3-butadiene) (iv) Inductive effect: The shifting of in electrons a o-bond due differences, electronegativity transmitted through the chain of atoms. Differentiate between

(i) Aliphatic and Aromatic hydrocarbons • Aliphatic: The compound that are not are aromatic called aliphatic hydrocarbons. (e.g. alkanes, alkenes, etc.). • Aromatic: It is a special class of cyclic hydrocarbons haring high carbon to hydrogen ratio and based on benzene and their benzene, derivatives (e.g. naphthalene etc.). (ii) Homolytic and Heterolytic Fission: • Homolytic: Bond breaks evenly, each atom gets one electron (forms free radicals). • Heterolytic: Bond breaks unevenly, one atom gets both electrons (forms ions). (iii) Electrophile and Nucleophile: • Electrophile: Electron-deficient species that accepts electrons (eg Ht). species that • Nucleophile: Electron-rich donates electrons (eg OH).

Alkanes do not undergo addition reactions because they are saturated hydrocarbons with strong C-C and C-H sigma bonds, which are relatively non- reactive. is reaction 04. How elimination considered the opposite of an addition reaction. an elimination reaction, Ans. In atoms/ groups are removed from a molecule, forming a double bond. It is the reverse of to addition reactions, where atoms groups are added to a molecule, breaking a double bond.

See Q.6 from theory.

See Q.8 from theory. Uses of

2-butene forms a more stable secondary carbocation, while propene forms a less stable primary carbocation. Thus, the carbocation in 2-butene is more stable due to greater alkyl group stabilization.

See Q.11,12 from theory.

Structural of CsHio (alkenes): (i) Pent-1-ene (ii) Pent-2-ene (ili) 2-Methylbut-1-ene (iv) 2-Methylbut-2-ene (v) 3-Methylbut-1-ene

See Q.11,13 from theory.

2-bromopropane is favored due to the Markovnikov's rule. In HBr addition, the more stable secondary carbocation intermediate forms (at C-2), leading to 2- bromopropane

Conjugated alkenes show different reactivity due to electron delocalization over alternating double bonds, making them more stable and reactive in specific conditions like Diels-Alder reactions.

Inductive effect of alky groups stabilizes carbocations by pushing electron density toward the positively charged carbon atom, reducing its charge intensity the equation for each

Reaction equations: 250°C→ CH,CH,CH = CH, + H, - (i) CH,CH,CH,CH, (ii) CH,CH = CH, + Ch, c4 →CH,CH(CICH,Cl (ili) CH,CH,CH = CHCH,CH, + H2O- 11350, > CH,CH,CH(OH)CH, CH, CH

(1) Isobutylene (ii) 2,3,4,4-Tetramethyl-2- pentene (iii) 2 ,5-Heptadiene (iv) 4,5- Dimethyl-2-hexene (v) Vinylacetylene (vi) 1,3-Pentadiene (vii) 1-Butyne (viii). 3-n- Propyl-1, 4-pentadiene (ix) Vinyl bromide (x) But-1 -en.3 - yne (xi) 4-Methyl-2-pentyne (XII) Isopentane Structural formulas (i) Isobutylene CH, = C-CH, (I) 2,3,4,4-Tetramethyl-2-pentene CH3 H3C - C= C - C-CH CH, CH, CH, (iii) 2,5-Heptadiene CH3-CH=CH-CH2-CH=CH-CH3 (iv) 4,5-Dimethyl-2-hexene CH, - CH = CH-CH- CH-CH, CH, CH, (v) Vinylacetylene CH2=CH-C=CH (Vị)-1,3-Pentadiene CH2=CH-CH=CH-CH3 (vil) 1-Butyne CH=C-CH2-CH3 (vili) 3-n-Propyl-1,4-pentadiene CH, = CH-CH-CH = CH, - CH, CH, CH, (ix) Vinyl bromide CH2=CH-Br (x) But-1-en-3-yne CH2=CH-C=CH (xi) 4-Methyl-2-pentyne CH, - C= C-CH- CH3 CH3 (X11) Isopentane CH, - CH-CH, - CH, CH,

Hex-2-ene (ii) (CH)C=CH, 2-Methylpropene fr CH- CH, -CH, -C= CH, (iii) CH(CH3)2 2-Iso-propyl-1-pentene (iv) CH,= CH-CH=CH2 1,3-Butadiene CH = C-CH,CH,CH3 (V) C,HS 2-Etheyl-1-pentene SLO BASED SHORT QUESTION ANSWERS

Hydrocarbons are organic compounds composed only of carbon and hydrogen atoms. They are classified into: • Alkanes (saturated hydrocarbons) • Alkenes (unsaturated with one or more double bonds) (VI) (CH,CH2)3 CH 3-Ethylpentane (vii) CH,CH,C(CH,)2CH(CH, CH,)CH, 3,3,4-Trimethylhexane (Vill)CH, = CH-C=C-CH= CH, 1,5-Hexadien-3-yne (ix) (CH), CH-CH, - C(CH3)3 2,2,4-Irimethylpentane (x) CH, = CH-C= CH 1-Buten-3-yne (xi) CH C(CH.)(CH,)CH, 2,2- Dimethylbutane HзC-CH,-СH-CH›-CH,CH3 (xii) H,C- CH 3-Ethylhexane (CH3)2CH-CH- CH(CH3)2 (хіїї) CH3 2,3,4-Trimethylpentane CH 3 (XIV) H3C-CH, - CH2-CH CH3 2-Methylpentane • Alkynes (unsaturated with one or more triple bonds) (contain • Aromatic hydrocarbons benzene rings) Example • Methane (CH4) - alkane • Ethene (CzH4) - alkene • Ethyne (CHz) - alkyne • Benzene (C6H6) - aromatic

Alkanes are saturated hydrocarbons with single covalent bonds between carbon atoms. Their names are based on the number of carbon atoms using Greek/Latin prefixes and end in "-ane" Example • CH4 - Methane • CHo - Ethane • CзН8 - Propane

Alkanes show chain isomerism, where compounds have the same molecular formula but different carbon chain arrangements. Example • C4H1o → n-butane and isobutane (2- methylpropane) alkanes called are

Alkanes are called paraffins (Latin: "little affinity") meaning parum affinis because they are less reactive due to strong C-C and C-H bonds and absence of functional groups.

Halogenation is the substitution reaction where hydrogen atoms are replaced by halogens in the presence of heat or UV light. Example CH4 + Cl → CH:Cl + Hcl (in UV light)

unsaturated hydrocarbons with at least one double bond between carbon atoms. General formula: CnH2n Example • Ethene: C2H4 • Propene: C3Нь show alkenes do

Alkenes show: • Chain isomerism • Position isomerism (location of double bond) • Geometrical (cis-trans) isomerism due to restricted rotation of the double bond Example But-2-ene exists as cis-but-2-ene and trans- but-2-ene

Markovnikov's Rule states that in the addition of HX to an alkene, the hydrogen more with to the carbon attaches hydrogens, and halogen attaches to the carbon with fewer hydrogens. Example CH3-CH=CH2 + HBr → CH3-CHBr-CH3 (2-bromoprópane)

Due to the presence of a triple bond with high electron density, alkynes are more reactive in addition reactions than alkanes. an of example

Benzene (C.H6) has a hexagonal ring with alternating double bonds. It where electrons are shows resonance, delocalized over the ring.

Benzene avoids addition to preserve aromatic stability. Substitution maintains the delocalized i system.

Boiling point increases with molecular size due to greater van der Waals forces. Branching lowers the boiling point. Example • n-butane > isobutane

Hydrocarbons are non-polar, thus insoluble in water but soluble in organic solvents like ether and benzene.

No, most hydrocarbons are less dense than water and float on it. They have more empty space than water

Incomplete combustion produces soot, monoxide (CO) and carbon contributing to air pollution, greenhouse effect, and acid rain (from sulfur/nitrogen compounds).

Butane is a fuel used is lighters. Isobutene is used as a propellant in products such as shaving gel.