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Stereoisomerism models

Draw Fischer projections or make molecular models of the four stereoisomeric 3 ammo 2 butanols and label each erythro or threo as appropriate... [Pg.302]

Hydrogenation of 3-carene is, in principle, capable of yielding two stereoisomeric products. Write their structures. Only one of them was actually obtained on catalytic hydrogenation over platinum. Which one do you think is formed Explain your reasoning with the aid of a drawing or a molecular model. [Pg.277]

Fig. 6.11. Representation of transition structure and die LUMO orbitals for three stereoisomeric complexes of A-acryloyloxazolidinone with a TADDOL model, Ti[0(CH2)40]Cl2. The LUMO energies (B3LYP/6-3111+G(d)) in kcal/mol. Reproduced from J. Org. Chem., 63, 2321 (1998), by permission of the American Chemical Society. Fig. 6.11. Representation of transition structure and die LUMO orbitals for three stereoisomeric complexes of A-acryloyloxazolidinone with a TADDOL model, Ti[0(CH2)40]Cl2. The LUMO energies (B3LYP/6-3111+G(d)) in kcal/mol. Reproduced from J. Org. Chem., 63, 2321 (1998), by permission of the American Chemical Society.
While the sizes of the atoms are not proportionately correct, the models are useful to represent the arrangement of the atoms according to their bond angles. The models also demonstrate structural isomerism and stereoisomerism. [Pg.169]

The dissection of a molecular model into those components that are deemed to be essential for the understanding of the stereochemistry of the whole may be termed factorization (9). The first and most important step toward this goal was taken by van t Hoff and Le Bel when they introduced the concept of the asymmetric carbon atom (10a, 1 la) and discussed the achiral stereoisomerism of the olefins (10b,lib). We need such factorization not only for the enumeration and description of possible stereoisomers, important as these objectives are, but also, as we have seen, for the understanding of stereoselective reactions. More subtle differences also giving rise to differences in reactivity with chiral reagents, but referable to products of a different factorization, will be taken up in Sect. IX. [Pg.185]

In order to apply this rule we had to transform the original three-dimensional structural formula in two stages (Fig. 5). In the first, the ligand model, the sequences of atoms constituting the ligands of an element of stereoisomerism... [Pg.209]

But even when the constitution of the polymer may be regarded as essentially homogeneous, considerations analogous to the previous ones may apply at the stereochemical level. For this reason the study of macromolecular stereoisomerism calls for a twofold approach. On the one hand, one must turn to ideal models that permit the identification of the type of structure existing in the polymer on the other, statistical criteria must be used to determine to what... [Pg.3]

Tertiary carbon atoms along the chain have been defined as asymmetric (22-25, 34-37), pseudoasymmetric (6, 10, 38-40), stereoisomeric centers (30, 31), and diasteric centers (41). The first two terms put the accent on chirality and are linked to the use of models of finite and infinite length, respectively the last two consider only phenomena of stereoisomerism. Note the relationship between these last definitions and Mislow s and Siegel s recent discussion (42), where the two concepts—stereoisomerism (or stereogenicity) and chirality—are clearly distinguished. The tertiary carbon atoms of vinyl polymers are always stereogenic whether they are chinotopic or achirotopic (42) depends on stmctural features and also on the type of model chosen (43). [Pg.6]

The problem is further complicated for vinyl polymers with their problems of stereoisomerism. The first descriptions of the conformational state of isotactic polypropylene in solution go back 25 years (178, 179, 192, 193). Corradini, Allegra, and Ganis proposed a model, still essentially valid today, according to which macromolecules possess a local helical structure analogous to that observed in the crystalline state. The helix segments are rather short, only a few monomer units, after which an inversion of the helix sense occurs, with simultaneous alteration of its direction (Figure 15). As a whole this disordered con-... [Pg.56]

Further model-building experiments have shown that an a helix can form in polypeptides consisting of either L- or D-amino acids. However, all residues must be of one stereoisomeric series a D-amino acid will disrupt a regular structure consisting of L-amino acids, and vice versa. Naturally occurring L-amino acids can form either right- or left-handed a helices, but extended left-handed helices have not been observed in proteins. [Pg.120]

Molecular models of the four stereoisomeric aldotetroses may be viewed on Learning By Modeling. [Pg.1036]

Fig. 4.17 illustrates the potential of carbon-13 NMR to detect the presence of isotactic (a), syndiotactic (b), and atatactic (c) vinyl polymers with polypropylene as sample [521], The spectrum of atactic polypropylene (Fig. 4.17(c)) displays the signals of all possible stereosequences including iso- and syndiotactic ones. Using the empirical increment systems for alkane carbon shift prediction [85, 201, 202] and including y effects of Zy = — 5 ppm specifically obtained by analysis of stereoisomeric polypropylene partial sequences between 3,5-dimethylheptane and 3,5,7,9,11,13,15-heptamethylheptadecane as a heptad model, the methyl carbon-13 shifts of all 36 possible heptads can be calculated... [Pg.309]

If you have a set of molecular models with which you can make or use bent bonds for double bonds, construct each of the following molecules and determine if stereoisomerism is possible and, if so, identify the type of stereoisomers. [Pg.145]


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