Alkyl halides properties

Many of the properties of alcohols and alkyl halides are affected by whether then-functional groups are attached to primary secondary or tertiary carbons We will see a number of cases m which a functional group attached to a primary carbon is more reac live than one attached to a secondary or tertiary carbon as well as other cases m which the reverse is true... 

Physical Properties of Alcohols and Alkyl Halides Intermolecular Forces... 

Relatively simple notions of attractive forces between opposite charges are suffi cient to account for many of the properties of chemical substances You will find it help ful to keep the polarity of carbon-oxygen and carbon-halogen bonds m mind as we develop the properties of alcohols and alkyl halides m later sections... 

PHYSICAL PROPERTIES OF ALCOHOLS AND ALKYL HALIDES INTERMOLECULAR FORCES... 

The properties of organometallic compounds are much different from those of the other classes we have studied to this point Most important many organometallic com pounds are powerful sources of nucleophilic carbon something that makes them espe cially valuable to the synthetic organic chemist For example the preparation of alkynes by the reaction of sodium acetylide with alkyl halides (Section 9 6) depends on the presence of a negatively charged nucleophilic carbon m acetylide ion... 

Aryl halides resemble alkyl halides m many of their physical properties All are practi cally insoluble m water and most are denser than water... 

Pyrazoles, isoxazoles and isothiazoles with a hydroxyl group in the 3-position (491 Z = NR, O, S) could isomerize to 3-azolinones (492). However, these compounds behave as true hydroxy derivatives and show phenolic properties. They give an intense violet color with iron(III) chloride and form a salt (493) with sodium hydroxide which can be O-alkylated by alkyl halides (to give 494 R = alkyl) and acylated by acid chlorides (to give 494 R = acyl). 

Triflates of aluminum, gallium and boron, which are readily available by the reaction of the corresponding chlorides with triflic acid, are effective Fnedel-Crafis catalysis for alkylation and acylation of aromatic compounds [119, 120] Thus alkylation of toluene with various alkyl halides m the presence of these catalysts proceeds rapidly at room temperature 111 methylene chloride or ni-tromethane Favorable properties of the triflates in comparison with the correspond mg fluorides or chlorides are considerably decreased volatility and higher catalytic activity [120]... 

Organolithium compounds are sometimes prepared in hydrocarbon solvents such as pentane and hexane, but nonnally diethyl ether is used. It is especially important that the solvent be anhydrous. Even trace amounts of water or alcohols react with lithium to form insoluble lithium hydroxide or lithium alkoxides that coat the surface of the metal and prevent it from reacting with the alkyl halide. Furthennore, organolithium reagents are strong bases and react rapidly with even weak proton sources to fonn hydrocarbons. We shall discuss this property of organolithium reagents in Section 14.5. 

The 4,5-dihydro compounds (34) might be expected to show different properties. Here, as with the pyrazolines discussed in Section IV, A, lone pairs of electrons should be available on both nitrogen atoms for reaction to give salts of type 35 and/or 36. No salts of type 35 have been reported. Indeed, the reaction between the alkyl halide... 

These reactions may be considered to be a method of obtaining 1,3,2,5-dioxaborataphosphoniarinanes with different substituents at carbon and phosphorus atoms of the ring. Comparing the properties of cyclic oxyalkyl-phosphines and boryloxyalkylphosphines, it should be noted that in both cases the reaction with alkyl halides results in the formation of a tertiary phosphonium salt. The reaction with electrophilic reagents such as diphe-nylchlorophosphine and diphenylchloroborane proceeded quite differently [Eq. (100)]. 

If ion pairs but not free ions are formed, the extent of ion pair formation may be estimated from the dielectric properties of the solution. This method has been used in studying the effect of Lewis acids on alkyl halides.164... 

As esters the alkyl halides are hydrolysed by alkalis to alcohols and salts of halogen acids. They are converted by nascent hydrogen into hydrocarbons, by ammonia into amines, by alkoxides into ethers, by alkali hydrogen sulphides into mercaptans, by potassium cyanide into nitriles, and by sodium acetate into acetic esters. (Formulate these reactions.) The alkyl halides are practically insoluble in water but are, on the other hand, miscible with organic solvents. As a consequence of the great affinity of iodine for silver, the alkyl iodides are almost instantaneously decomposed by aqueous-alcoholic silver nitrate solution, and so yield silver iodide and alcohol. The important method of Ziesel for the quantitative determination of alkyl groups combined in the form of ethers, depends on this property (cf. p. 80). 

Alcohols, alkyl halides, ethers, and amines all have functional groups with single bonds. These compounds have many interesting uses in daily life. As you learn how to identify and name these compounds, think about how the intermolecular forces between their molecules affect their properties and uses. 

In this section, you learned how to recognize, name, and draw members of the alcohol, alkyl halide, ether, and amine families. You also learned how to recognize some of the physical properties of these compounds. In the next section, you will learn about families of organic compounds with functional groups that contain the C=0 bond. 

The polarity of carbon-halogen bond of alkyl halides is responsible for their nucleophilic substitution, elimination and their reaction with metal atoms to form organometallic compounds. Nucleophilic substitution reactions are categorised into and on the basis of their kinetic properties. Chirality has a profound role in understanding the reaction mechanisms of Sj l and Sj 2 reactions. Sj 2 reactions of chiral all l halides are characterised by the inversion of configuration while Sj l reactions are characterised by racemisation. 

Recent work (Brown and Pearsall, 15) has indicated that while hydrogen aluminum tetrachloride is nonexistent, interaction of aluminum chloride and hydrogen chloride does occur in the presence of substances (such as benzene and presumably, olefins) to which basic properties may be ascribed. It may be concluded that while hydrogen aluminum tetrachloride is an unstable acid, its esters are fairly stable. Further evidence in support of the hypothesis that metal halides cause the ionization of alkyl halides (the products of the addition of the hydrogen halide promoters to the olefins) is found in the fact that exchange of radioactive chlorine atoms for ordinary chlorine atoms occurs when ferf-butyl chloride is treated with aluminum chloride containing radioactive chlorine atoms the hydrogen chloride which is evolved is radioactive (Fair-brother, 16). 

Water, alcohols, acids, anhydrides, and esters have varying chain-transfer properties [Mathie-son, 1963]. The presence of any of these transfer agents in sufficient concentrations results in Reaction 5-28 becoming the dominant mode of termination. Termination by these compounds involves transfer of HO, RO, or RCOO anion to the propagating carbocation. Aromatics, ethers, and alkyl halides are relatively weak chain-transfer agents. Transfer to aromatics occurs by alkylation of the aromatic ring. 

---