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Ring large

Table 8 presents structures observed for monocyclic dienes and polyenes with rings large enough to accommodate trans C=C double bonds. In a cyclodecadiene molecule strain-free carbon skeletons can only be derived when two double bonds are diametrically placed and have the same configuration (as, cis or trans,trans). Cw,cis-Cyclodeca-1,6-diene (1,6-CDD) may exist in twelve different conformations, and it is therefore noteworthy that it almost exclusively prefers one of these, namely the one indicated in Table 8. This conformer does not have the repulsive transannular HH interactions that destabilize the corresponding saturated molecule in all conceivable conformers. Table 8 presents structures observed for monocyclic dienes and polyenes with rings large enough to accommodate trans C=C double bonds. In a cyclodecadiene molecule strain-free carbon skeletons can only be derived when two double bonds are diametrically placed and have the same configuration (as, cis or trans,trans). Cw,cis-Cyclodeca-1,6-diene (1,6-CDD) may exist in twelve different conformations, and it is therefore noteworthy that it almost exclusively prefers one of these, namely the one indicated in Table 8. This conformer does not have the repulsive transannular HH interactions that destabilize the corresponding saturated molecule in all conceivable conformers.
In five-membered rings large negative deviations from additivity have been observed as well (315,322,323). In eclipsed c/j-glycols the ICS values can be as large as - 15 (315,322) they are somewhat smaller if vicinal bromo, azido, or acetamido substituents are involved. As a rule, upfield ICSs are palpably reduced in the trans isomers (322,323), especially for carbon atoms bearing less electronegative substituents, such as Br, SH, and N3. [Pg.278]

Rubber ring, large - sliding bowl bottom Sliding bowl bottom... [Pg.73]

A study of the intramolecular alkoxymercuration of ( )-5-arylpent-4-en-l-ols (70) has indicated that the regioselectivity is closely related to the Hammett constants of the para-substituents on the benzene ring. Large solvent effects on the regioselectivity were also observed (Scheme 17 and Tables 2 and 3). By contrast, the related oxymercuration of -methylstyrene is 100% a-sclcctivc. This comparison shows that the regioselectivity of the intermolecular reaction is controlled by electronic factors, whereas the cyclization is governed by a delicate balance of steric and electronic effects.65... [Pg.406]

Inthe A-ring, small substituents (e.g., OH, OCH, Cl, ethynyl) are tolerated at aU four positions (395, 396), and have less impact on intrinsic activity than that of substituents in the N-2 phenyl ring. Large substituents are tolerated only at the 8-position, as indicated by the high affinity of the benzyloxy derivative (68) (396). The other three positional isomers... [Pg.560]

Chiraldex G -DA Aromatic amines containing 2 or more rings, large eyelie diols. Some heterocyclics, multi-ring compounds and those with bulky substituents. [Pg.445]

At the transition state a considerable positive charge is distributed on the benzene ring, largely at carbon atoms 2, 4, and 6 relative to the entering bromine atom ... [Pg.168]

Alternatively, enantioselective nucleophilic addition to imines followed by intramolecular trapping of the transient amino intermediate with creation of a new C-N bond constitutes a powerful strategy for the synthesis of various heterocycles of synthetic and biologic interest. In this field, the formation of six-membered rings largely leads the way, and one of the first examples was reported in 2(X)3 by Ohsawa s group [4a] for the direct synthesis of the 3-carboline core via a Mannich/aza-Michael cascade promoted by (5)-proline and subsequentiy applied to the total synthesis of e t-dihydrocorynantheol (Scheme 16.3) [4b]. [Pg.560]

Reviews this year include a very extensive account of the photochemistry and spectroscopy of Py-unsaturated carbonyl compounds, the chemistry of excited triplet carbonyl compounds, the first of a two-part review of the photochemistry of the benzene ring (largely photoisomerization reactions), photochemical and thermal isomerizations of l-acylcyclopent-2-enes and 5-acylbicyclo[2,l,0]pentanes, and thione photochemistry. As noted last year, the coverage of this section is necessarily brief, and the reader is reminded of the companion report on photochemistry. One or two references could not comfortably be allocated to the various sub-sections below, and are reported here. [Pg.289]


See other pages where Ring large is mentioned: [Pg.324]    [Pg.300]    [Pg.181]    [Pg.441]    [Pg.61]    [Pg.502]    [Pg.59]    [Pg.73]    [Pg.382]    [Pg.502]    [Pg.834]    [Pg.834]    [Pg.406]    [Pg.210]    [Pg.181]    [Pg.25]    [Pg.72]    [Pg.212]    [Pg.204]    [Pg.339]    [Pg.140]    [Pg.42]    [Pg.348]    [Pg.170]    [Pg.359]    [Pg.17]    [Pg.427]    [Pg.206]    [Pg.365]    [Pg.29]    [Pg.313]    [Pg.573]    [Pg.270]    [Pg.834]    [Pg.230]    [Pg.1321]    [Pg.297]   
See also in sourсe #XX -- [ Pg.81 , Pg.88 , Pg.90 , Pg.110 , Pg.112 ]

See also in sourсe #XX -- [ Pg.81 , Pg.88 , Pg.90 , Pg.110 , Pg.112 ]




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18-membered ring structures, large pore zeolite

18-membered ring structures, large pore zeolite molecular sieves

18-membered ring structures, large pore zeolite silicates

Annulenes large ring

Aromatics large-ring carbocycles

Chelate ring large

Conformation medium and large rings

Cyclic acetylenes large-ring

Cyclic polyenes, large-ring

Cycloaddition large rings formation

Cycloalkane rings Large

Cyclodextrins large-ring

Electronic spectra of large-ring heterocyclic compounds

FUSION TO ORDINARY AND LARGE RINGS

Ketone, alicyclic large ring

Lactones large-ring

Large Ring Complexes

Large Ring Systems

Large ring compound

Large ring forgings

Large ring heterocycles

Large ring synthesis

Large rings aromaticity

Large rings basicity

Large rings conformation

Large rings metal complexes

Large rings radical attack

Large rings reactivity

Large rings structure

Large rings tautomerism

Large rings transannular interactions

Large rings, definition

Large rings, reviews

Large-membered ring lactone

Large-ring acetylenes

Large-ring acetylenes strained

Large-ring acetylenes synthesis

Large-ring carbocycles

Large-ring lactone

Large-size rings free-energy correction terms

Medium and large rings

Medium- and Large-ring Compounds

Medium- and large-ring lactones

Natural product synthesis large ring formations

Nuclear magnetic resonance small and large rings

Of large ring compounds

Reactivity of Small and Large Rings

Ring compounds, large, synthesis

Ring compounds, large, synthesis considerations

Rings small, medium and large, definitions

Seven-membered, Medium, and Large Rings

Special Topic 6.14 Photochemical synthesis of large rings

Structure of Small and Large Rings

Synthesis of Polyhydroxylated Carbocyclic Derivatives with Large Rings

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