Halogen Derivatives - incomplete

halogenoalkane: halogen bonded to sp3 hybridised C atom halogenoarenes: halogen derivatives of arenes (X directly bonded to benzene ring)

(chloromethyl) benzene Brackets for the chloro cuz it’s not bonded directly to the benzene ring

Primary - 1 R attached to the C atom bearing the halogen Secondary - 2 R “ Tertiary - 3 R “

BP: - BP of halogenoalkanes RX (pdpd & idid) > corresponding alkane (idid) • For halogenoalkanes RX with the same X [/R], bp increases as the size of R [/X] increases. As the size of R [/X] increases, there is a larger and more polarisable e- cloud as the no. of e- per molecule increases. Hence, strength of idid increases Solubility: • Poor solubility in water - altho they are non polar, they are not able to interact with water molecules via hydrogen bonding. • Soluble in organic solvents - able to interact with these solvent molecules via idid forces Density: Density increases as X increaeses and atomic no. of X larger = denser - fluoroalkanes & monochloroalkanes are less dense than water - in general, chloroalkanes with 2 or more Cl atoms, bromoalkanes & iodoalkanes are denser than water

Alkanes, alkenes and alcohols

R-H + X2 ————–> R-X + HX R&C: X2 (limiting), uv light/sunlight/heat M: Free-radical substituation Not a very gd method as poly-substitution can occur, leading to a mixture of products. Using limiting amt of X2 helps to minimise poly-substitution

• halogenoalkane with only 1 halogen atom per molecule C=C + HX (g) ————> C - C | | H X R&C: dry gaseous HX, rm temp Mechanism: electrophilic addition • halogenoalkane with 2 adjacent halogen atoms per molecule C=C + X2 —————–> C - C | | X X R&C: X2 in CCl4, rm temp Mechanism: electrophilic addition • can form mixed halogen too - less electronegative one will be δ+ eg CH2=CH2 + IBr ——-> CH2ICH2Br R&C: IBR in CCL4, rm temp Mechanism: electrophilic addition

• dry HX, heat E.g. R-OH +HBr ——–> R-Br + H2O • PX3 *anhydrous condition must be used becuz PX3 reacts with water E.g. 3R-OH + PBr3 ——–> 3R-Br + H3PO3 E.g. 3R-OH + PI3 — red P, I2 —-> 3R-I + H3PO3 • PCl5 E.g. R-OH + PCl5 ———-> R-Cl + POCl3 + HCL *Test for alcohol -OH grp: white fumes of hydrogen chloride, which turns damp blue litmus paper red • SOCl2 *sometimes preferred cuz prod. are gases, easy to remove E.g. R-OH + SOCl2 ————> R-Cl + SO2 + HCl R-OH —> R-Cl | PCl5 or SOCl2, rm temp R-OH —> R-Br | PBr3 or dry HBr, heat R-OH —> R-I | red P, I3

Is a species that is able to donate an e- pair to an electron-deficient atom to form a covalent bond

the C-X bond in R-X is polar as the halogen atom is more electronegative than the carbon atom, hence the C atom has a partial +ve charge and is said to be e- deficient

SN2: Kinetics: rate is directly prop to [OH-] Stereochemistry: Enantiomerically pure reactant gives enantiomerically pure prod Since the overall order of rctn is 2, it involves both halogenoalkane and nucleophile in the slow single step. Hence, we can conclude that the rctn is single-step and bimolecular. SN1: Kinetics: rate is independent of [OH-] (Order of rctn is 1) Stereochemistry: Enantiomerically pure reactant gives racemic mixture of prod Since the overall order of rctn is 1, it involves only halogenoalkane in the slow step. Hence, we can conclude that the rctn is more than 1 step and unimolecular.

S stands for substitution N stands for nucleophilic 2 stands for 2 rct particles involved in the rate determining step (bimolecular) Nucleophilic attack: • In the halogenoalkane molecule, the C-X bond is polar with the C atom acquiring a partial +ve charge since it is less electronegative than the halogen atom. • During the rctn, the nucleophile attacks the partially positively charged C atom from the side DIRECTLY OPP the halogen atom (backside attack) • In the transition state, there is simultaneous partial formation of C-Nu bond and partial cleavage of the C-X bond Checklist: • name of mechanism • δ+ on C & δ- on X • lone pair of e- on Nu- • curly arrows to show flow of e- • inverted prod (inversion of configuration)

Xδ+ blocks the approach of the nucleophile from the front side. It also repels the nucleophile since both are e- rich

• Strength of carbon-halogen bond The weaker the bond (R-I), the faster the reaction X NOT dependent on mag. of the partial positive charge on the carbon in the C-X bond • Steric effect of R grps in SN2 rctns less steric hindrance around the C bonded to the X atom (1° halogenoalkane) = more reactive