Libido rule

Jencks libido rule [9, 10] attempts to identify situations in which proton transfer can be expected to be concerted with the making or breaking of covalent bonds "Concerted general acid-base catalysis of complex reactions in aqueous solution can occur only (a) at sites that undergo a large change in pK in the course of the reaction, and (b) when this change in pK converts an unfavorable to a favorable proton transfer with respect to the catalyst i.e., the pK of the catalyst is intermediate between the initial and final pK values of the substrate site. [9]. 

New systems designed to test this conclusion confirm the central importance of the intramolecular hydrogen bond. Note that the proton transfer in mechanism 3.2 follows Jencks libido rule, evolving from strongly unfavorable in the reactant to strongly favorable in the product so the hydrogen bond could be dose to its strongest in the transition state. 

Use the libido rule to predict which of the following acids could give specific catalysis or general catalysis in the following reaction (the pX., of the conjugate acid of an imine is around 4 to 5) HCl, picric acid, acetic acid, ammonium, and phenol. 

Headache and GI symptoms are the most frequently reported side effects. It is possible to reduce GI side effects, such as nausea, abdominal discomfort, and diarrhea, by taking the extract with food. Theoretically, decreased libido or erectile dysfunction could also occur. Because of saw palmetto s possible hormonal effects (and lack of indications for use), pregnant and nursing women should avoid it. It is important to rule out prostate cancer in those taking saw palmetto for BPH, since the symptoms are similar. The effect of saw palmetto on prostatic cancer would likely be beneficial but not curative. No drug interactions have been reported. 

SKF 7690 (43a), caused sterility in mice after 35 days of treatment with a dally dose of 12.5 mg.°° Spermatogenesis was not effected but decreased libido and reduction in reproductive capacity have not been ruled out. 3-Chloro-l,2-propanedlol (U-5897) caused reversible sterility in rats, guinea pigs and monkeys.6 u-5897 may produce a local ischemia resulting... 

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