16 quotes found
"There's enough alcohol in one year's yield of an acre of potatoes to drive the machinery necessary to cultivate the fields for one hundred years."
"I would trade all my experimental works for the single idea of the benzene theory."
"In the benzene nucleus we have been given a soil out of which we can see with surprise the already-known realm of organic chemistry multiply, not once or twice but three, four, live or six times just like an equivalent number of trees. What an amount of work had suddenly become necessary, and how quickly were busy hands found to carry it out! First the eye moves up the six stems opening out from the tremendous benzene trunk. But already the branches of the neighbouring stems have become intertwined, and a canopy of leaves has developed which becomes more spacious as the giant soars upwards into the air. The top of the tree rises into the' clouds where the eye cannot yet follow it. And to what an extent is this wonderful benzene tree thronged with blossoms! Everywhere in the sea of leaves one can spy the slender hydroxyl bud: hardly rarer is the forked blossom [Gabelblüte] which we call the amine group, the most frequent is the beautiful cross-shaped blossom we call the methyl group. And inside this embellishment of blossoms, what a richness of fruit, some of them shining in a wonderful blaze of color, others giving off an overwhelming fragrance."
"People have wracked their brains for an explanation of benzene and how the celebrated man [Kekulé] managed to come up with the concept of the benzene theory. With regard to the last point especially, a friend of mine who is a farmer and has a lively interest in chemistry has asked me a question which I would like to share with you. My 'agricultural friend' apparently believes he has traced the origins of the benzene theory. 'Has Kekulé,' so ran the question, 'once been a bee-keeper? You certainly know that bees too build hexagons; they know well that they can store the greatest amount of honey that way with the least amount of wax. I always liked it,' my agricultural friend went on, 'When I received a new issue of the Berichte; admittedly, I don't read the articles, but I like the pictures very much. The patterns of benzene, naphthalene and especially anthracene are indeed wonderful. When I look at the pictures I always have to think of the honeycombs of my bee hives.'"
"We have demonstrated by exploiting an Armediated approach that (H2O)6− undergoes type I →II interconversion in the process of complex formation with benzene."
"Methylbenzene is readily metabolized because its methyl C – H bonds are relatively weak with respect to homolytic and heterolytic cleavage. When one of these methyl hydrogens has been removed, the resulting phenylmethyl (benzyl)group, C6H5CH2, may be viewed as a benzene ring whose p system overlaps with an extra porbital located on an attached alkyl carbon. This interaction, generally called benzylic resonance,stabilizes adjacent radical, cationic, and anionic centers in much the same way that overlap of a pbond and a third porbital stabilizes 2-propenyl (allyl) intermediates (...). However, unlike allylic systems, which may undergo transformations at either terminus and give product mixtures (in the case of unsymmetrical substrates), benzylic reactivity is regioselective and occurs only at the benzylic carbon. The reason for this selectivity lies in the disruption of aromaticity that goes with attack on the benzene ring."
"Phenols and their ethers are ubiquitous in nature; some derivatives have medicinal and herbicidal applications, whereas others are important industrial materials. (...) phenols are stronger acids because of the neighboring aromatic ring."
"When a benzene ring bears enough strongly electron-withdrawing substituents, nucleophilic addition to give an intermediate anion with delocalized charge becomes feasible, followed by elimination of the leaving group (nucleophilic aromatic ipso substitution). Phenols result when the nucleophile is hydroxide ion, arenamines (anilines) when it is ammonia, and alkoxyarenes when alkoxides are employed. Very strong bases are capable of eliminating HX from haloarenes to form the reactive intermediate benzynes, which are subject to nucleophilic attack to give substitution products. Phenols may also be prepared by decomposition of arenediazonium salts in water and by Pd-catalyzed hydroxylations of haloarenes."
"The electronic structure of the three heterocycles pyrrole, furan, and thiophene is similar to that of the aromatic cyclopentadienyl anion. The cyclopentadienyl anion may be viewed as a butadiene bridged by a negatively charged carbon whose electron pair is delocalized over the other four carbons. The heterocyclic analogs contain a neutral atom in that place, again bearing lone electron pairs. One of these pairs is similarly delocalized, furnishing the two electrons needed to satisfy the 4n + 2 rule."
"The steric interaction between any axial substituent and a β-situated heteroatom is counted as zero. Thus, in 3-substituted tetrahydropyrans, the destabilization due to an axial R substituent is computed as half of the AR. … The anomeric effect refers to the tendency of a group X at C(1) of a pyranose ring to assume the axial rather than the equatorial orientation. This phenomenon is important in carbohydrate chemistry since it influences the composition of isomeric mixtures and hence their reactivities. … The anomeric effect is solvent and substituent dependent …"
"The alkaloids are bitter-tasting, natural nitrogen-containing compounds found particularly in plants. The name is derived from their characteristic basic properties (alkali-like), which are induced by the lone electron pair of nitrogen. As with acyclic amines, the (Lewis) basic nature of the alkaloids, in con junction with their particular three-dimensional architecture, gives rise to often potent phys iological activity. We have already noted some examples of this behavior in the narcotics morphine and heroin, the psychoactive lysergic acid and LSD, and the antibiotic penicillins."
"Alkyl halides are not often found in terrestrial organisms, but the kinds of reactions they undergo are among the most important and well-studied reaction types in organic chemistry. ... Simple alkyl halides can be prepared by radical halogenation of alkanes, but mixtures of products usually result. ... Alkyl halides can also be prepared from alkenes by reaction with N-bromosuccinimide (NBS) to give the product of allylic bromination. ... Alcohols react with HX to form alkyl halides, but the reaction works well only for tertiary alcohols, R3COH. ... Alkyl halides also react with lithium metal to form organolithium reagents, RLi. In the presence of CuI, these form diorganocoppers, or Gilman reagents (LiR2Cu)."
"Simple aromatic hydrocarbons come from two main sources: coal and petroleum. Coal is an enormously complex mixture made up primarily of large arrays of benzene-like rings joined together. Thermal breakdown of coal occurs when it is heated to 1000 °C in the absence of air, and a mixture of volatile products called coal tar boils off. Fractional distillation of coal tar yields benzene, toluene, xylene (dimethylbenzene), naphthalene, and a host of other aromatic compounds. Unlike coal, petroleum contains few aromatic compounds and consists largely of alkanes. (...) During petroleum refining, however, aromatic molecules are formed when alkanes are passed over a catalyst at about 500 °C under high pressure."
"The most utilized Umpolung strategy is based on formyl and acyl anion equivalents derived from 2-lithio- 1,3-dithiane species. These are readily generated from 1,3-dithianes (thioacetals) because the hydrogens at C(2) are relatively acidic (pKa~31)."
"The α-hydrogens of nitroalkanes are appreciably acidic due to resonance stabilization of the anion … The anions derived from nitroalkanes give typical nucleophilic addition reactions with aldehydes (the Henry-Nef tandem reaction). Note that the nitro group can be changed directly to a carbonyl."
"The question of a possible physiological significance, in the resemblance between the action of choline esters and the effects of certain divisions of the involuntary nervous system, is one of great interest, but one for the discussion of which little evidence is available. Acetyl-choline is, of all the substances examined, the one whose action is most suggestive in this direction. The fact that its action surpasses even that of adrenaline, both in intensity and evanescence, when considered in conjunction with the fact that each of these two bases reproduces those effects of involuntary nerves which are absent from the action of the other, so that the two actions are in many directions at once complementary and antagonistic, gives plenty of scope for speculation."