Optically inactive compounds

Obviously, in a relatively small work such as this it is not possible to be comprehensive. Preparations of bulk, achiral materials (e.g. simple oxiranes such as ethylene oxide) involving key catalytic processes will not be featured. Only a handful of representative examples of preparations of optically inactive compounds will be given, since the emphasis in the main body of this book, i.e. the experimental section, is on the preparation of chiral compounds. The focus on the preparation of compounds in single enantiomer form reflects the much increased importance of these compounds in the fine chemical industry (e.g. for pharmaceuticals, agrichemicals, fragrances, flavours and the suppliers of intermediates for these products). 

These reactions have been extensively studied for optically inactive compounds of silicon and first row transition-metal carbonyls. ... 

A reaction in which an optically inactive compound (or achiral center of an optically active moledule) is selectively converted to a specific enantiomer (or chiral center). See Asymmetric Induction... 

An example of a compound whose chiral discrimination poses the utmost difficulty is a saturated quaternary hydrocarbon bearing similar substituents on the asymmetric carbon atom, with a representative example being 5-ethyl-5-propylundecane,i.e., (n-butyl)ethyl(n-hexyl)(n-propyl)methane (Fig. 8) [ 106]. The enantiomer of this hydrocarbon exhibits practically no optical rotation ( of < 0.001) between 280 and 580 nm. The compound is a chiral, but to all intents an optically inactive, compound. To the best of our knowledge, the chirality of this compound has not been discriminated using any current method. Mislow called such hidden chirality cryptochirality [ 14,107]. 

Uleine methiodide underwent a facile Hofmann degradation to give an optically inactive compound (CCXLVIII), which retained the two nitrogen atoms and had carbazole UV-absorption. A further Hofmann degradation eliminated Nb and gave a product (CCXLIX) with somewhat extended carbazole absorption, which underwent ready catalytic reduction with saturation of one double bond to give a substituted... 

Two optically inactive compounds are possible structures for compound X. 

The addition of piperidine to (+)-l-methyl-4-[(l-methylethenyl)sulfinyl]benzene (17) is very slow, in accordance to the reactivity of the corresponding sulfone towards amines50. Furthermore, the yield of the adduct obtained from reactions in ethanol at 80 °C for 1 week is only 55%. The remainder is unchanged sulfoxide, together with optically inactive compounds which are not sulfoxides. H-NMR spectroscopy of the l-[2-(4-methylphenyl-sulfinyl)propyl]piperidine 18 showed a d.r. of64 36, corresponding to an optical purity of 29 %. This figure is tentative because of the modest yield of adduct obtained, as well as the lack of information on whether there is any selectivity between diastereomers in the formation of byproducts. 

We highlight here a few studies in which the synthesis of chiral molecules has been achieved through the use of organic crystals in the hopes that this will prove a useful incentive and review. The reported studies fall into two natural categories. In the one case one starts with racemic mixtures or optically inactive compounds, crystallize these materials into chiral crystals and finally by subsequent reactions, trap this chirality in the final chemical products. In the second category one forms host-guest inclusion compounds in which the host is already an optically resolved compound. This in turn leads to the formation of optically active guest molecules. 

Theory of van t Hoff-LeBel.—Two men independently of each other advanced a theory which explains these facts. One, a Dutch chemist by the name of van t Hoff, and the other a French chemist, LeBel. On examining the structural formulas of optically active compounds these men each saw that they differed in a common way from all optically inactive compounds which were not possible of being split into optical components. Taking as an illustration the alcohol with which we are dealing, viz., active amyl alcohol or 2-methyl butanol-1 we see by examining its formula that one of the carbon atoms is characteristically different from all of the others. 

Dry distillation of the methohydroxide of CCCLXVI led to a series of optically inactive compounds, the ultraviolet spectra of which resemble that of /S-phenyl naphthalene. They were identified as... 

A new optically inactive compound, murrayacine, C18H15O2N (mp 244°) has been isolated. Spectral examination suggested that this substance is a 3-formylcarbazole and zinc dust distillation gave carbazole. Its dihydro derivative on reduction with lithium aluminum hydride furnished a compound CigHigON (mp 176°) which was identical with dihydrogirinimbine LXXXVIIh. Murrayacine is therefore LXXXVIIg 146). 

Terpineol (CioHigO) is an optically active compound with one asymmetric carbon. It is used as an antiseptic. Reaction of terpineol with H2/Pt forms an optically inactive compound (C10H20O). Heating the reduced compound in acid followed by ozonolysis and work-up under reducing conditions produces acetone and a compound whose NMR and NMR are shown. What is the structure of terpineol ... 

An optically active monoterpene (compound A) with molecular formula CioHjgO undergoes catalytic hydrogenation to form an optically inactive compound with molecular formula C10H20O (compound B). When compound B is heated with acid, followed by reaction with O3, and workup under reducing conditions (Zn, H2O), one of the products obtained is 4-methylcyclohexanone. Give possible structures for compound A. 

Evidence for an intermediate epoxide was obtained by reacting the salt 31 in dimethylformamide with sodium hydride to give an optically inactive compound shown by NMR spectroscopy to be epoxide 37 racemization was assumed to occur via the zwitterion 36. Treatment of the epoxide with sodium hydroxide furnished the optically inactive diol 34 by a process thought to involve direct attack of hydroxide ion on the epoxide ring An alternative mechanism for this reaction is proposed later (see Section III, F), and other features of the epoxide route are also discussed. The diol 33 from ribalinium salt was also obtained as a mixture of the (-) and (+) enantiomers (ratio, 4.4 1), and a corresponding epoxide pathway may also be involved. 

Pasteur s other main important discovery, among many others in this field, was the resolution of sodium ammonium racemate, an optically inactive compound, by crystallization (1848-1850). In describing his discovery, he remarks ... 

The two inactive forms of a dipeptide are obtained when the two optically inactive compounds are coupled together by synthesis, and they appear first in the form of the corresponding halogen derivative,... 

Evidence of chirality, then, is a mark of distinction between substances. This provides another reason in support of the thesis that isotopic variants are distinct substances in conflict with the 1923 lUPAC ruling. Kokke and Oossterhoff (1972, 1973), for example, have shown that substitution of oxygen-18 for the more common oxygen-16 isotope in an optically inactive compound gives rise to chiral effects. The substitution of deuterium for protium gives rise to a similar but more marked chiral effect. 

Meso compound (Section 5.12B) An optically inactive compound whose molecules are achiral even though they contain tetrahedral atoms with four different attached groups. 

Compound A is an optically inactive compound with a molecular formula of CsHg. Catalytic hydrogenation of A gives an optically inactive compound, B (C5H10), as the sole product. Furthermore, reaction of A with HBr results in a single compound, C, with a molecular formula of CgHgBr. Provide structures for A, B, and C. 

There is a totally different manner in which infrared spectroscopy is applied to study macromolecular conformations. Here, researchers make use of what is known as infrared dlchroism. In the next chapter we will be discussing the phenomenon called circular dichroism. Circular dichroism means the difference in the absorption of right- and left-handed circularly polarized light by an optically active compoimd. The phenomenon used in infrared dichroism is not circular dichroism. One can refer to this as linear dichroism. This phenomenon means that molecules oriented in one direction will absorb plane polarized light differently when the electric vector of the light is parallel to the orientation of the molecule and when it is perpendicular to this orientation. Whether the compound is optically active or not is of no consequence to this phenomenon even optically inactive compounds will show linear dichroism. 

When D-galactose is heated in the presence of nitric acid, an optically inactive compound is obtained. Draw the structure of the product and explain why it is optically inactive. 

The most important compound is wyo-inositol, (1Z,2Z,3Z,5Z, 4 ,6 )-cyclohexane-l,2,3,4,5,6-hexol, formerly also called meso-inositol (or i-inositol, phaseomannitol, nucitol, bios I, mouse antialopaecia factor or vitamin Bjjj). The affix myo was preferred to the affix meso as it defines a certain configuration of hydroxyl groups above and below the plane of the ring (1,2,3,574,6-), while the second affix has a general meaning and is used to label achiral, optically inactive compounds with the same number of identically bound enantiomeric groups. 

A Wohl degradation is done on a monomethyl ether of D-idose. The product, when oxidized with nitric acid, gives an optically inactive compound. At what position of idose is the methyl ether located ... 

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