Compounds containing a hydroxyl group attached to a benzene ring are called phenols. Derivatives of phenols, such as naphthols and phenanthrols, have chemical properties similar to those of phenols, as do most of the many naturally-occurring substituted phenols. Like other alcohols, phenols have higher boiling points than hydrocarbons of similar molecular weight. Like carboxylic acids, phenols are more acidic than their alcohol counterparts. Phenols undergo a number of different reactions; both their hydroxyl groups and their benzene rings are highly reactive. A number of chemical tests can be used to distinguish phenols from alcohols and carboxylic acids.Thymol, a naturally occurring phenol, is an effective disinfectant that is obtained from thyme oil. Thymol can also be synthesized from m-cresol, as shown in Reaction A below. Thymol can then be converted to menthol, another naturally-occurring organic compound; this conversion is shown in Reaction B.Reaction AReaction B The reaction of phenol with dilute nitric acid produces which of the following compounds?
Answer(s): A
To answer this question, you need to know that hydroxyl groups are electron-donating and so they activate aromatic rings towards electrophilic aromatic substitution. Like all electrondonating groups, hydroxyl groups are ortho-para directors. So in this case, the nitro group will add to phenol to form two products, ortho-nitrophenol and para-nitrophenol. This means choice A is the correct answer. Choice B, which has only para-nitrophenol, is incomplete and therefore wrong. Choices C and D can be eliminated because they both include meta- nitrophenol, which will NOT be formed. The only way to get meta-nitrophenol would be to start with nitrobenzene and turn it into a phenol, which would work because the nitro group is an electron-withdrawing, deactivating meta director. The reaction will produce only negligible amounts of meta-nitrophenol, if any.
Compounds containing a hydroxyl group attached to a benzene ring are called phenols. Derivatives of phenols, such as naphthols and phenanthrols, have chemical properties similar to those of phenols, as do most of the many naturally-occurring substituted phenols. Like other alcohols, phenols have higher boiling points than hydrocarbons of similar molecular weight. Like carboxylic acids, phenols are more acidic than their alcohol counterparts. Phenols undergo a number of different reactions; both their hydroxyl groups and their benzene rings are highly reactive. A number of chemical tests can be used to distinguish phenols from alcohols and carboxylic acids.Thymol, a naturally occurring phenol, is an effective disinfectant that is obtained from thyme oil. Thymol can also be synthesized from m-cresol, as shown in Reaction A below. Thymol can then be converted to menthol, another naturally-occurring organic compound; this conversion is shown in Reaction B.Reaction AReaction B What simple chemical test could be used to distinguish between the following two compounds?
Answer(s): B
Compound I is para-cresol or para-methylphenol, and Compound II is benzyl alcohol, which behaves more like an aliphatic alcohol than a phenol. We can take advantage of this fact in order to distinguish between these two compounds. One of the easiest ways to do this is by their solubility behavior, which is also an easy way of separating them out of a mixture. Phenols are appreciably acidic, so they are quite soluble in aqueous sodium hydroxide. Alcohols, including benzyl alcohol, are NOT acidic and won't be soluble in aqueous sodium hydroxide. Now there is one exception; very small alcohols, with fewer than five carbons, are water-soluble, so they would dissolve in ANY aqueous solution. However, benzyl alcohol is too big a molecule to be water- soluble, so it won't be soluble in sodium hydroxide solution. So, the solubility of paracresol, Compound I, in aqueous sodium hydroxide would provide an effective test to distinguish between the two compounds, and thus choice B is the correct answer. Notice that this means you could separate a mixture of these two compounds by dissolving it in an organic solvent, and then extracting the solution in a separatory funnel with aqueous layer.Choice C is wrong, because compound I won't react with a bromine solution and decolorize it. Both compounds will react under stronger conditions, namely, the presence of a Lewis acid, but bromine in solution is too mild a reagent to react with the stable aromatic ring. Therefore, compound I, and compound II for that matter, won't decolorize bromine solution and choice C is incorrect. Choice D is incorrect because neither of the two compounds will be soluble in sodium bicarbonate. Sodium bicarbonate is a weak base, but since phenols are fairly weak acids, it takes a fairly STRONG base to make a phenol give up its acidic proton. Thus, para-cresol won't dissolve in sodium bicarbonate. As we've said, benzyl alcohol is an even weaker acid than para-cresol, so it certainly won't dissolve in sodium bicarbonate. And since neither compound will be soluble in sodium bicarbonate, sodium bicarbonate can't be used to distinguish between them.
Compounds containing a hydroxyl group attached to a benzene ring are called phenols. Derivatives of phenols, such as naphthols and phenanthrols, have chemical properties similar to those of phenols, as do most of the many naturally-occurring substituted phenols. Like other alcohols, phenols have higher boiling points than hydrocarbons of similar molecular weight. Like carboxylic acids, phenols are more acidic than their alcohol counterparts. Phenols undergo a number of different reactions; both their hydroxyl groups and their benzene rings are highly reactive. A number of chemical tests can be used to distinguish phenols from alcohols and carboxylic acids.Thymol, a naturally occurring phenol, is an effective disinfectant that is obtained from thyme oil. Thymol can also be synthesized from m-cresol, as shown in Reaction A below. Thymol can then be converted to menthol, another naturally-occurring organic compound; this conversion is shown in Reaction B.Reaction AReaction BCompound × (C10H14O) dissolves in aqueous sodium hydroxide but is insoluble in aqueous sodium bicarbonate. The proton NMR spectrum of compound X is as follows:1.3 (9H)singlet4.8 (1H)singlet7.1 (4H) MultipletWhich of the following is the structure of Compound× ?
All four answer choices are aromatic compounds, so Compound X must be aromatic. The chemical formula for this compound consists of carbons, hydrogens, and oxygens (which means you can eliminate choice C immediately, since that contains bromine atoms). The next piece of information in the question is that Compound X is soluble in aqueous sodium hydroxide, but not in aqueous sodium bicarbonate. This eliminates choice A, which is a substituted benzoic acid which WOULD certainly dissolve in sodium bicarbonate. From our discussion in the previous question, you should remember that the ability to dissolve in aqueous sodium hydroxide, but NOT in aqueous sodium bicarbonate, is characteristic of phenols. This suggests that Compound X is a phenol, which would make choice B correct and choice D, which is a phenyl ether, incorrect. But there's other information in this passage, so you should check through it to see if it supports your preliminary conclusion. Now let's look at the NMR spectrum and see what information we can get from that. The NMR spectrum has three separate peaks. The multiplet of area four has a chemical shift of 7.1, which is very far upfield; this represents the aromatic ring, and is due to the spin-spin coupling of four aromatic hydrogens. The signal at a chemical shift of 1.3 has a peak area of 9 hydrogens; the chemical shift indicates carbon-hydrogen single bonds, and the fact that there are nine hydrogens that are all equivalent means that this represents a tert-butyl group. This would fit EITHER choice B or choice D. And finally, the second singlet peak, whose chemical shift is 4.8 has an area of one. If Compound X were choice D, the single hydrogen peak that you'd get would be from the -CH group of the tert-buyl, next to the ether-group oxygen; this would be much further downfield, probably with a chemical shift of about 2.3 or 2.4, so choice D must be wrong. The fact that the signal from the single hydrogen is shifted much further upfield, to 4.8, indicates that the proton involved is deshielded, which in turn suggests that it's attached to a more elec-tronegative element than carbon. This magnitude of shift is in fact characteristic of a phenolic hydrogen. This agrees with our previous conclusion, that Compound X is choice B, and so B is the correct answer, as we suspected before.
A certain drug inhibits ribosomal RNA synthesis. Which of the following eukaryotic organelles would be most affected by the administration of this drug?
This question tests your knowledge of both cell structure and function. You are presented with an unlabeled figure of a cukaryotic cell and asked to determine which of the four numbered structures would be most affected by a drug that inhibits ribosomal RNA synthesis. So basically, you have to know which structure is involved in the synthesis of ribosomal RNA. The nucleolus is the organelle responsible for ribosomal RNA synthesis, and in figure, structure 1 is the nucleolus, and so choice A is correct. Structure 2 is the nucleus; structure 3 is the Golgi apparatus; and structure 4 is a mitochondrion.
Exocrine secretions of the pancreas:
Answer(s): D
An exocrine gland is one that excretes its products into tubes or ducts that typically empty onto epithelial tissue, while an endocrine gland is one that releases hormones directly into the bloodstream. The pancreas functions both as an endocrine gland and an exocrine gland. As an endocrine gland it produces and secretes three hormones; insulin, glucagon, and somatostatin. Insulin lowers blood glucose levels by stimulating the uptake of glucose onto tissues, and its subsequent conversion into its storage form. glycogen. So, choice B is wrong.Choice A is incorrect because it's glucagon that raises blood glucose levels by stimulating the conversion of glycogen into glucose. Somatostatin suppresses both insulin and glucagon secretion. Choice C is incorrect because thyroid hormones are involved in the regulation of metabolic rate.As an exocrine gland, the pancreas secretes enzymes that are involved in protein, fat, and carbohydrate digestion; all of its exocrine products are secreted into the small intestine. Pancreatic amylase hydrolyzes starch to maltose; trypsin hydrolyzes peptide bonds and catalyzes that conversion of chymotrypsinogen to chymotrypsin; chymotrypsin and carboxypeptidase also hydrolyze peptide bonds; and finally, lipase hydrolyzes lipids.
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