Ethers acid-base chemistry

A. Amat, F. De Angelis, A. Sgamellotti, and S. Fantacci, Acid-base chemistry ofluteoUn and its methyl-ether derivatives A DFT and ab initio investigation, Chem. Phys. Lett. 462 (2008), pp. 313-317. 

Chapters 1—10 begin a study of organic compounds by first reviewing the fundamentals of covalent bonding, the shapes of molecules, and acid-base chemistry. The structures and typical reactions of several important classes of organic compounds are then discussed alkanes, alkenes and alkynes, haloalkanes, alcohols and ethers, benzene and its derivatives, and amines, aldehydes, and ketones, and finally carboxylic acids and their derivatives. 

Ethers are unreactive to many reagents used in organic chemistry, a property that accounts for their wide use as reaction solvents. Halogens, dilute acids, bases, and nucleophiles have no effect on most ethers. In fact, ethers undergo only one reaction of general use—they are cleaved by strong acids. Aqueous HBr and HI both work well, but HCl does not cleave ethers. 

In carbohydrate chemistry, the preparation of ethers that are stable in the presence of acids, bases, and aqueous alkali is an important analytical and synthetic tool. The methods used for the etherification of hydroxyl groups51 generally employ reactions of unprotected sugars and glycosides with methyl, allyl, benzyl, triphenylmethyl, and alkylsilyl halides in the presence of a variety of aqueous and nonaqueous bases. 

Lewis acids are thus electron-deficient molecules or ions such as BF-, or carbo-cations, whereasTewis bases are molecules or ions containing available electrons. such as amines, ethers, alkoxide ions, and so forth.,A Lewis acid-base reaction is the combination of an acid and a base to form a complex, or adduct. The stabilities of these adducts depend on the structures of the constituent acid and base and vary over a wide range. Some examples of Lewis acid—base reactions are given in Table 3.19. Lewis acid-base reactions abound in organic chemistry ... 

This chapter is primarily concerned with keto-enol equilibrium and the chemistry of dissociated enols (enoxides) and lithium enolates. The acid-base aspects of the chemistry of other metal enolates (e.g. silyl enol ethers "", boron enol ethers" " " , aluminium , tin " , gallium , bismuth , zinc " ", rhodium , palladium " , manganese ", copper , nickel , magnesium " , titanium " , molybdenum , zirconium" " and ammonium" " enolates) have been reported elsewhere. 

Activated carbon, in keeping with the enhanced complexity of carbon-based chemistry, possesses an extensive array of surface moieties, including hydroxyl groups, carboxylic acid groups, aldehyde groups, keto groups, cyclic ethers, and lactone groups. 

Where is the term for water in the first set of equations In general chemistry, the water is removed from the equation to simphfy calculations. However, when water is removed from the equilibrium constant equation, this act also removes the base from the acid-base equation. If water is not the solvent and there is a different base in the reaction, the base certainly must be put back in the equation. In other words, the equilibrium constants for the formic acid reaction with ether as well as the methanol and HCl reaction must use the Kg equations ... 

As suggested earlier, the Lewis acid-Lewis base process is not limited to carbocations. In iodomethane (65), bond polarization makes the carbon 6+. If this carbon atom reacts with a nucleophile, it is an electrophilic carbon. This reaction uses a specific nucleophile—methoxide ion—in which the two-electron donor is the oxygen atom. Note that the methoxide ion is the conjugate base formed when methanol (1) reacts with a suitable base. The reaction forms a new C-0 bond and breaks the C-I bond. Remember that carbon can only have four bonds, so if a new C-0 bond is formed, one must break. The bond that breaks is the weaker polarized C-I bond. The final products of this reaction are ether 66 and the iodide ion. Using the fundamental principles of Lewis acid-Lewis base chemistry and knowing that the carbon is polarized and reacts with an electron-rich species allows a prediction of the product of this reaction. This reaction is known as a nucleophilic substitution (see Sn2 reactions in Chapter 11, Section 11.2). 

Developments in ab initio MO quantum chemistry have resulted in theoretical models [41]. These are able to predict the properties of neutral molecules and ions within so-called chemical accuracy (about 2 kcal/mol). This makes these procedures extremely useful in ion chemistry, especially in thermochemical studies. Another approach is DFT that has attracted intense interest. DFT offers the promise of less drastic scaling with the size of the system than traditional ab initio methods. In general, hybrid density functions frequently provide the best overall agreement and surpass MP2 result of ab initio theory. There have been a number of theoretical studies of the structures and binding energies of alkali ions to many bases, including from free radical, biradical, amino acid, and crown ether to DNA bases (see details in Chap. 3). 

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