Backside treatment

Reaction of the same starting material 15-2 with ethyl formate and sodium ethoxide, as in the case of the desalkyl series, proceeds to form the 2-formyl derivative 17-1 (Scheme 5.17). Exhaustive catalytic hydrogenation then gives the 2a-methyl derivative dromostanolone (17-2). The initial product, as in the case of the desoxy series, consists of the 2)8-methyl derivative from approach of hydrogen from the open backside. Treatment with base epimerizes this to the favored 2a-methyl epimer 17-3 (dromostanolone), in which the newly introduced methyl group is equatorial. 

Converters looking to improve corona treatment should consider high definition-type corona systems where optimized dielectrics are used to minimize these filaments, as well as the potential for pin-holing and backside treatment. 

In addition to these surface reactions, plasma also facilitates the use of chemical gases which can produce controlled chemical reactions on the surface as well. Plasma technology also eliminates the possibility for backside treatment. 

Surface quality Because ceramic is a crystalline solid with a flat-ground allows for any solid to create an surface, it will not typically deform. This means that the web substrate will always be in contact with the roll surface and eliminate any ingress of air which will cause backside treatment. 

The soft nature of the silicone rubber impression into the rubber, creating dents and pockets of air will cause backside treatment in a pattern matching the roll surface. 

Uneven web tensions are enough to stretch or thin within minutes, causing poor quality treatment and potential backside treatment. 

Epoxides are cleaved by treatment with acid just as other ethers are, but under much milder conditions because of ring strain. As we saw in Section 7.8, dilute aqueous acid at room temperature is sufficient to cause the hydrolysis of epoxides to 1,2-diols, also called vicinal glycols. (The word vicinal means "adjacent/ and a glycol is a diol.) The epoxide cleavage takes place by SK2-like backside attack of a nucleophile on the protonated epoxide, giving a trans- 1,2-dio) as product. 

Perhaps the single most important reaction of enolate ions is their alkylation by treatment with an alkyl halide or tosylate, thereby forming a new C-C bond and joining two smaller pieces into one larger molecule. Alkylation occurs when the nucleophilic enolate ion reacts with the electrophilic alkyl halide in an SN2 reaction and displaces the leaving group by backside attack. 

For example, the treatment of cfs-3-methylcyclohexanol with p-toluenesulfonyl chloride and pyridine forms a cis tosylate A, which undergoes backside attack by the nucleophile OCH3 to yield the trans ether B. 

The comment can be added that those of medical orthodoxy agree to certain protocols of treatment to protect their backsides. In other words, even if the treatment fails (or almost always fails), it will still be recognized (in court) by the attending physician s medical peers as the therapy of choice. Not necessarily so with alternatives, although a consent form is signed. 

No treatment of solvent effects on carbocationic reactivity that does not treat explicitly the anion-stabilizing effect should be acceptable (18), even for processes in which the rate-determining step is solvent attack on an ion pair. Probably, backside anion stabilization by the solvent intervenes even in the contact ion pair. In fact, rotation of the anion in this pair can deliver a molecule of solvent attached to the anion to the cation from the front thus, the predominant retention of configuration occasionally observed in the solvolysis products is explained. 

Estradiol and estrone are metabolized to an array of oxidized products, one of which consists of the 16a-hydroxy derivative 30-4. One approach to preparing that compound starts by reaction of estrone with isopropyhdene acetate, to afford the acetate of the enolic form of the ketone and also the ester of the phenol at position 3 (30-1) (Scheme 3.30). Treatment of that product with perbenzoic acid leads to the a-oxirane 30-2, formed from approach of the reagent from the less hindered backside. Acetolysis of that intermediate gives 16a-acetoxyestrone (30-3). Reaction of that product with lithium aluminum hydride leads to reduction of the 17-carbonyl and also the phenolic ester to give the trans-Aio 16a-hydroxy- 17(3-estradiol (30-4). The same product is obtained on reducing 30-2 directly also with lithium aluminum hydride. 

Attack from the more open backside leads to formation of the a-acetylide. Mild hydrolysis of the enol ether function then affords the unconjugated ketone ethynodrel (14-5), This first oral contraceptive to reach the market has become better known as The Pill . The double bond in that product moves into conjugation on treatment with strong acid, forming ethynodrone (14-6), the second contraceptive pill to reach pharmacy shelves. 

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