Optically active compounds formulae

NMR spectroscopy was found to be a valuable technique for differentiation between the enantiomers of optically active compounds. The principles of the methods used to distinguish between enantiomers by means of NMR have been developed and reviewed by Mis-low and Raban (217). The best results from the point of view of the determination of optical purity and absolute configuration of chiral sulfur compounds, especially of sulfinyl compounds, have been obtained with the help of chiral solvents (218). Pirkle (86) was the first to demonstrate that enantiomeric sulfoxides have nonidentical NMR spectra when dissolved in chiral alcohols having the following general formula ... 

Compound 58 was isolated as a yellow crystalline, optically active compound. HREIMS data for 58 gave a molecular formula of C15H16O4 with an inherent eight degrees of unsaturation. The IR spectrum was consistent with the presence of conjugated carbonyl functionalities including a y-lactone (1779 cm ) and a conjugated ketone (1665 cm ). The... 

The specific rotation of an optically active compound in a pure solvent may be calculated from the formula —... 

Make sure you have a comprehensive selection of data for all new compounds, including proof of molecular formula and of purity. Do not forget individual pieces of data that are easily overlooked, such as ir data and the specific rotation for optically active compounds. 

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. 

Asymmetric Carbon.—Now van t Hoff and LeBel found that all optically active compounds contained at least one such carbon atom. They ascribed the existence of two optically active forms to the presence in the compound of this uns3anmetrically related or asymmetric carbon atom. The asymmetry of the compounds, in that one form is dextrorotatory the other levo-rotatory, is due to this asymmetric arrangement of the molecule in space. We emphasized the fact that our structural formulas as we have been using them are simply plane representations of relationships, and indicate nothing as to the arrangement in space of the atoms or groups in a molecule. The theory of van t Hoff and LeBel considers the molecule as it is arranged in space. The isomerism so explained is known as stereo-isomerism or space isomerism. 

In order to convince oneself of the justice of these remarks it is necessary to run through the following list of optically active compounds in the formula of which the asymmetric carbon is indicated by C ... 

They can also indicate the sign of optical rotation in the formula or name of an optically active compound. 

IR-4.4.3.2 Formal treatment as coordination compounds IR-4.4.3.3 Chain compounds IR-4.4.3.4 Generalized salt formulae IR-4.4.3.5 (Formal) addition compounds IR-4.4.4 Figand abbreviations IR-4.5 Isotopically modified compounds IR-4.5.1 General formalism IR-4.5.2 Isotopically substituted compounds IR-4.5.3 Isotopically labelled compounds IR-4.5.3.1 Types of labelling IR-4.5.3.2 Specihcally labelled compounds IR-4.5.3.3 Selectively labelled compounds IR-4.6 Optional modibers of formulae IR-4.6.1 Oxidation state IR-4.6.2 Formulae of radicals IR-4.6.3 Formulae of optically active compounds IR-4.6.4 Indication of excited states IR-4.6.5 Structural descriptors IR-4.7 References... 

This chapter is organized in much the same manner as its predecessor, with some subsections expanded whenever warranted. Unless otherwise noted, the structural formulas of optically active compounds in this chapter represent their absolute configurations, and the numbering system employed for the benzo[n]quinolizidine alkaloids is identical with that used previously 1,12). 

Each optically active compound has a characteristic specific rotation. The specific rotation is the number of degrees of rotation caused by a solution of 1.0 g of the compound per mL of solution in a sample tube 1.0 dm long at a specified temperature and wavelength. The specific rotation can be calculated from the observed rotation using the following formula ... 

An extension of the structure theory serves to explain adequately the isomerism of the amyl alcohols and other optically active compounds. This extension takes into account the arrangement of the atoms in space. Many compounds are known which resemble the amyl alcohols in their action on polarized light. An examination of the structure of these compounds brings out the fact that they, in nearly all cases, contain a carbon atom to which are joined four different atoms or groups. Such a carbon atom is said to be asymmetric. In the case of active amyl alcohol there is one carbon atom which is in combination with the groups CH3, C2H6, H, and CH2OH. This asymmetric atom is marked with a in the formula... 

Threose, an isomer of erythrose, shows similar chemical behavior except that nitric acid oxidation yields an optically active compound of formula CiiHeOe. ... 

These two structures are enantiomers, (-) Threose i an isomer of (-) Erythrose with similar chemical properties. Oxidation of (-) Threose by nitric acid gives an optically active compound with the formula CtjHeOe. 

To differenciate the optically active compounds from the racemic ones described in the other sections, the former will be numbered differently. The numbers of the corresponding racemic compounds ate added in brackets in the formula schemes. 

Propose structures for compounds E-H. Compound E has the molecular formula CsHs and is optically active. On catalytic hydrogenation E yields F. Compound F has the molecular formula C5H10. is optically inactive, and cannot be resolved into separate enantiomers. Compound G has the molecular formula CgHio and is optically active. Compound G contains no triple bonds. On catalytic hydrogenation G yields H. Compound H has the molecular formula CeH, is optically inactive, and cannot be resolved into separate enantiomers. 

Make a reaction flowchart (roadmap diagram), as in previous problems, to organize the information provided to solve this problem. An optically active compound A (assume that it is dextrorotatory) has the molecular formula CyHuBr. A reacts with hydrogen bromide, in the absence of peroxides, to yield isomeric products, B and C, with the molecular formula C7Hi2Br2. Compound B is optically active C is not. Treating B with 1 mol of potassium rerr-butoxide yields (+)-A. Treating C with 1 mol of potassium rerr-butoxide... 

An optically active compound D has the molecular formula CeHio and shows a peak at about 3300 cm in its IR spectrum. On catalytic hydrogenation D yields E (CsHi4). Compound E is optically inactive and cannot be resolved. Propose structures for D and E. 

Corroborative evidence is often necessary from IR, which identifies the presence of many functional groups, and NMR, which confirms functional groups and, by spin-spin splitting patterns, the placement of these groups. Elemental analysis to determine the C, H, N, O, and heteroatom content is usually performed on pure compounds to assist in the assignment of an empirical formula. Optical activity measurements may be needed for chiral compounds. When used in conjunction with other analytical methods, such as elemental analysis, IR, and NMR, MS makes it possible to identify unknown compounds. Combined with a separation method like chromatography, as in GC-MS or LC-MS, even impure samples and mixtures can be analyzed and components identified. GC-MS and LC-MS are described in Chapters 12 and 13, respectively. 

An optically active compound. A, has a molecular formula of C6H12. Hydroboration-oxidation of A yields an optically active product, B, with a molecular formula of C6H14O. Catalytic hydrogenation of A yields an optically inactive product, C, with a molecular formula of CeHi4. Propose structures for A, B, and C. 

Draw a structural formula for an optically active compound with the molecular formula... 

When this is done, the structural formula of an optically active compound appears as the mirror-image of the formula of the corresponding epimeric compound. 

The D-aldopentose, (a), is oxidized to an aldaric acid, (b), which is optically active. Compound (a) undergoes a Ruff degradation to form an aldotetrose, (c), which imdergoes oxidation to an optically inactive aldaric acid, (d). What are the structural formulas of (a), (b), (c), and (d) ... 

X 16.101 cis-Platin is an anticancer drug with a structure jQ that can be viewed on the Web site, (a) What is the formula and systematic name for the compound cis-jf Platin (b) Draw any isomers that are possible for this compound. Label any isomers that are optically active, (c) What is the coordination geometry of the platinum atom ... 

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