Alkyl Halides and Aryl Halides Flashcards
Alkyl Halides
Alkyl halides are organic compounds that contain halogen atoms (fluorine, chlorine, bromine, or iodine) attached to an alkyl group. The general formula is R-X, where R represents the alkyl group and X is the halogen.
Aryl Halides
Aryl halides are organic compounds that contain a halogen atom bonded to an aromatic ring (aryl group). The general formula is Ar-X, where Ar represents the aryl group and X is the halogen.
Reactivity of Alkyl Halides
Alkyl halides are reactive due to the presence of the polar carbon-halogen bond. They undergo nucleophilic substitution and elimination reactions, making them essential in organic synthesis.
SN1 Reaction
SN1 (Substitution Nucleophilic Unimolecular) is a two-step nucleophilic substitution reaction involving the formation of a carbocation intermediate. It occurs in the presence of weak nucleophiles and is favored in the presence of polar protic solvents.
SN2 Reaction
SN2 (Substitution Nucleophilic Bimolecular) is a one-step nucleophilic substitution reaction where the nucleophile attacks the carbon attached to the leaving group, leading to a simultaneous bond-breaking and bond-making process. It is favored in the presence of strong nucleophiles and aprotic solvents.
Elimination Reactions
Elimination reactions involve the removal of a leaving group and a proton from adjacent carbon atoms to form a double bond or triple bond. The two common types are E1 (unimolecular elimination) and E2 (bimolecular elimination) reactions.
Sandmeyer Reaction
The Sandmeyer reaction is a method to convert aryl diazonium salts into different aryl halides using copper(I) halide as a catalyst. It is an essential reaction in the synthesis of aryl halides.
Lucas Reagent
HCl/ZnCl2. Used to produce R-Cl from alcohol. Also used in order to determine whether the carbocation in a reaction is primary, secondary, or tertiary, based on the rate of reaction (ppt formed). this test is called Lucas test.
Halogenation of Alkanes
Alkanes react with halogens (chlorine, bromine, or iodine) in the presence of heat or light to produce alkyl halides. The reaction involves the substitution of a hydrogen atom with a halogen atom.
Addition of Hydrogen Halides to Alkenes
Alkenes react with hydrogen halides (HCl, HBr, or HI) to produce alkyl halides. The hydrogen halide adds across the double bond, with the halogen attaching to one carbon and the hydrogen to the adjacent carbon.
Preparation of Alkyl Fluorides
Alkyl fluorides can be prepared by the reaction of alcohols with hydrogen fluoride (HF) or by the fluorination of alkyl halides using silver fluoride (AgF) as a fluorinating agent.
Preparation of Alkyl Chlorides and Bromides
Alkyl chlorides and bromides can be prepared by the reaction of alcohols with thionyl chloride (SOCl2) or phosphorous tribromide (PBr3), respectively. These reagents replace the hydroxyl group of alcohols with a halogen atom.
Preparation of Alkyl Iodides
Alkyl iodides can be prepared by the reaction of alcohols with red phosphorus and iodine (HI/P), known as the HI-P reduction method. This method replaces the hydroxyl group of alcohols with an iodine atom.
Halide Exchange Reactions
Finkelstein reaction. The Finkelstein reaction is a chemical reaction that involves the conversion of an alkyl halide to an alkyl iodide with the same alkyl group. It is a nucleophilic substitution reaction.
Swarts Reaction. The Swarts reaction is a chemical reaction that involves the conversion of an alkyl halide to an alkyl fluoride with the same alkyl group. It is a substitution reaction that uses metal fluorides such as AgF, Hg2F2, CoF2 or SbF3 as the nucleophile.
State of matter of Alkyl Halides
Alkyl halides can exist as liquids or solids at room temperature, depending on their molecular size and the strength of intermolecular forces. Those with smaller alkyl groups and halogens tend to be liquids, while larger ones are often solids.
Boiling Point of Alkyl Halides
Alkyl halides generally have higher boiling points compared to their parent alkanes due to the presence of polar carbon-halogen bonds. The boiling points increase with increasing molecular size and the atomic mass of the halogen.
Melting Point of Alkyl Halides
The melting points of alkyl halides are influenced by the size and nature of both the alkyl group and the halogen atom. Smaller alkyl halides with smaller halogens tend to have lower melting points, while larger ones have higher melting points.
Solubility of Alkyl Halides
Alkyl halides are generally insoluble in water due to the nonpolar nature of the alkyl groups. However, they are soluble in nonpolar organic solvents like diethyl ether, dichloromethane, and hexane.
Reaction with Metals
Alkyl halides can react with metals, such as lithium (Li) or magnesium (Mg), to form Grignard reagents.
Wurtz Reaction
The Wurtz reaction is a chemical reaction that involves the coupling of two alkyl halide molecules in the presence of metallic sodium (Na) to form a higher alkane.
Halogenation of Aryl halides
Anhydrous FeCl3 + X2 is used as a reagent. 1,4-Dihalobenzene(major) and 1,2-Dihalobenzene(minor) are formed.
Nitration of Aryl Halides
HNO3 and Conc. H2SO4 is used as a reagent. 1-Halo-2-nitrobenzene (Minor) and 1-Halo-4-nitrobenzene (Major) are formed.
Sulphonation of Aryl Halides
Conc. H2SO4 is used with heat as a reagent. 2-Halobenzenesulfonic acid (minor) and 4-Halobenzenesulphonic acid (major) are formed.
Friedel-Crafts reaction
Anhydrous AlCl3 is used as a reagent.
Alkylation- 1-Halo-2-alkylbenzene (minor) and 1-halo-4-alkylbenzene (major) are formed.
Acylation- 2-Haloacetonephenone (minor) and 4-Haloacetophenone (major) are formed.
