a.The isoelectric point is pH at which the net charge on the molecules in solution is0 b.The isoelectric point ispH at which the charge of the alpha-amino groups equals the charge on the alpha-earboxyl groups .The isoelectric point is pHat which the a-carboxyl and a-amino groups are uncharge d.Band Care correct e.A and Bare correct 19.Reaction of an unknown compound with acidic potassium permanganate yields a carboxylic acid and CO:;the unknown compound is a.a tetra-substituted alkene b.adisubstituted alkyne c.a tri-substituted alkene d.a terminal alkene with one alkyl substituent e.a trans,disubstituted alkene 20.Which of the following is true regardingS reactions: a.concurrent El elimination reactions are common b.rearrangement of the carbocation c.the reaction is favored by polar,protic solvents d.a and e only are both correct e.a,b and e are all correct 21.In order for a molecule to be aromatic: a.it must be planar,cyclic and consist of adjacent sp2 atoms containing 4n+2 -electrons b.it must have at least two electrons in each of the degenerate molecular orbitals describing the 元-system c.heteroatoms (must rehybridize so that all unshared pairs of electrons can contribute to the π-system d.a and b only are both true e.a,b and e are all correct 22.The B-sheet conformation ofa protein can be considered an example of. a.Primary structure b.Secondary structure c.Tertiary structure d.Quaternary structure 23.Which of the compounds shown below will react with methyl formate(methyl methanoate)in the presence of methoxide anion(CH)to give a compound,which on treatment with aqueous acid and gentle heating.will decarboxylate to form butanal? a 0、 第3页共6列 第 3 页 共 6 页 a. The isoelectric point is pH at which the net charge on the molecules in solution is 0 b. The isoelectric point is pH at which the charge of the alpha-amino groups equals the charge on the alpha-carboxyl groups c. The isoelectric point is pH at which the α-carboxyl and α-amino groups are uncharged d. B and C are correct e. A and B are correct 19. Reaction of an unknown compound with acidic potassium permanganate yields a carboxylic acid and CO2; the unknown compound is: a. a tetra-substituted alkene b. a disubstituted alkyne c. a tri-substituted alkene d. a terminal alkene with one alkyl substituent e. a trans, disubstituted alkene 20. Which of the following is true regarding SN1 reactions: a. concurrent E1 elimination reactions are common b. rearrangement of the carbocation intermediate is common c. the reaction is favored by polar, protic solvents d. a and c only are both correct e. a, b and c are all correct 21. In order for a molecule to be aromatic: a. it must be planar, cyclic and consist of adjacent sp2 atoms containing 4n+2 -electrons b. it must have at least two electrons in each of the degenerate molecular orbitals describing the -system c. heteroatoms（杂原子）must rehybridize so that all unshared pairs of electrons can contribute to the -system d. a and b only are both true e. a, b and c are all correct 22. The β-sheet conformation of a protein can be considered an example of: a. Primary structure b. Secondary structure c. Tertiary structure d. Quaternary structure 23. Which of the compounds shown below will react with methyl formate (methyl methanoate) in the presence of methoxide anion(CH3O- ) to give a compound, which on treatment with aqueous acid and gentle heating, will decarboxylate to form butanal? a. c. d. b. O O Br Br O O O O e