A study of the reactions of 2-Aryl-3,3-dimethylbicyclo[2,2,1]heptan-2-ols with acid

1978 ◽  
Vol 31 (8) ◽  
pp. 1747 ◽  
Author(s):  
JM Coxon ◽  
PM Projer ◽  
PJ Steel ◽  
ID Rae ◽  
AJ Jones
Keyword(s):  
Perchloric Acid ◽  
Low Temperatures ◽  
Chemical Shifts ◽  
Strong Acid ◽  
Fluorosulfonic Acid ◽  
Controlled Conditions

The 13C and 1H N.M.R. spectra of a series of 2-aryl-3,3- dimethylbicyclo[2,2,1]hept-2-yl cations generated in strong acid at low temperatures are reported. The chemical shifts of carbons proximate to the cation centres are discussed with reference to related cations. At higher temperatures, 2-aryl-3,3-dimethylbicyclo[2,2,1]hept-2-yl cations in fluorosulfonic acid give substituted 7,8-dimethyltetracyclo- [7,4,0,02,7,04,8]trideca-1(9),10,12-trienesulfonyl fluorides. Substituted 7,8-dimethyltetracyclo[7,4,0,-02,7,04,8]trideca-1(9),10,12-trienes and 7,8-dimethyltetracyclo[7,4,0,02,7,04,8]trideca-1(9),10,12-triene were prepared from 2-aryl-3,3-dimethylbicyclo[2,2,1]heptan-2-ols by reaction with perchloric acid under carefully controlled conditions.

15N N.M.R. Study of Some Palladium(II) Ammine Complexes

1988 ◽  
Vol 41 (9) ◽  
pp. 1425 ◽  
Author(s):  
TG Appleton ◽  
JR Hall ◽  
SF Ralph ◽  
CSM Thompson
Keyword(s):  
Perchloric Acid ◽  
Chemical Shifts ◽  
Free Ammonia ◽  
Silver Ion ◽  
Single Peak ◽  
Donor Atom ◽  
Ammine Complexes ◽  
Initial Product ◽  
Aqueous Perchloric Acid ◽  
Dimethylformamide Solution

Palladium(II) ammine complexes enriched in 15N give sharp singlets in their 15N n.m.r . spectra. The 15N chemical shifts depend primarily on the trans donor atom, in a qualitatively similar way to those for platinum(II) ammine complexes. A dimethylformamide solution of Pd(NH3)2Cl2 prepared in the usual way gave a single peak, consistent with the presence of only one isomer (trans). Reactions of increasing amounts of aqueous perchloric acid with Pd(NH3)42+ allowed peaks to be identified for Pd(NH3)3(H2O)2+, cis -Pd(NH3)2(H2O)22+ and Pd(NH3)(H2O)32+. The initial product of the reaction of trans-Pd(NH3)2Cl2 with silver ion is trans-Pd(NH3)2(H2O)22+, which rapidly disproportionates to Pd(NH3)3(H2O)2+ and Pd(NH3)(H2O)32+. With standing, subsequent reactions ultimately produce a solution containing predominantly cis -Pd(NH3)2(H2O)22+ in equilibrium with small amounts of the tri- and mono-ammine complexes, and free ammonia.

Seasonal distribution of dry-matter production in grass varieties from different latitudes in northern Europe

1985 ◽  
Vol 105 (1) ◽  
pp. 187-188 ◽  
Author(s):  
R. K. M. Hay
Keyword(s):  
Low Temperatures ◽  
Dry Matter ◽  
Field Experiments ◽  
Seasonal Distribution ◽  
Dry Matter Production ◽  
Northern Europe ◽  
British Isles ◽  
Controlled Conditions ◽  
Matter Production

Work in controlled conditions (Cooper, 1964; østgård & Eagles, 1971) has indicated that, under short photoperiods and low temperatures, Scandinavian grass varieties tend to grow more slowly than those from lower latitudes, and are, therefore, more resistant to cold and freezing stresses. This has been confirmed in field experiments (Håbjørg, 1979). These grasses would therefore be expected to cease growth earlier in the autumn when grown in the British Isles. However, this mechanism does not appear to operate under lengthening days; indeed, there is evidence to suggest that their growth is particularly stimulated by the combination of cool temperatures and long days (Cooper, 1964; Hay & Heide, 1983, 1984). This raises the possibility that varieties from Norway and Sweden could produce more dry matter than grasses of more southern provenance in the spring in upland areas, when low temperatures are associated with rapidly lengthening photoperiod (12·5–15 h) and moderate to high levels of irradiance (> 200 W/m2) (Hay, 1985).

A Possible Role for Abscisic Acid in Controlling Dormancy in Jojoba Flower Buds

1985 ◽  
Vol 12 (5) ◽  
pp. 463 ◽  
Author(s):  
A Benzioni ◽  
RL Dunstone
Keyword(s):  
Abscisic Acid ◽  
Water Stress ◽  
Low Temperatures ◽  
Water Status ◽  
Effect Of Temperature ◽  
Flower Buds ◽  
Controlled Conditions ◽  
Effects Of Temperature ◽  
Delayed Flowering ◽  
Endogenous Aba

Jojoba flower buds break dormancy in response to low temperatures in the presence of adequate water. The possibility that abscisic acid (ABA) is involved in the regulation of dormancy was examined by following endogenous ABA levels in flower buds and leaves and by applying synthetic (�)-ABA. Under controlled conditions endogenous levels of ABA were high in dormant flower buds and decreased under conditions of low temperatue that led to flowering. Similar results were obtained in the field. Levels in the leaves were low and changes in response to environmental treatments were small. Daily spraying of the plants with water containing 0.01% Tween enhanced flowering while water stress inhibited it. The application of (�)-ABA delayed flowering and reduced the percentage of flowers open at the end of the experiment. An experiment aimed at distinguishing between the effects of temperature and of water status was inconclusive and part of the effect of temperature on ABA may be related to the effect of temperature on the water status of plant.

The preparation and rearrangements of some 8,8-dimethylhomotropylium cations and their iron tricarbonyl complexes

1985 ◽  
Vol 63 (2) ◽  
pp. 418-425 ◽  
Author(s):  
Ronald F. Childs ◽  
Aravamuthan Varadarajan
Keyword(s):  
Low Temperatures ◽  
Chemical Shifts ◽  
Major Product ◽  
Membered Ring ◽  
Tricarbonyl Complex ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Free Energy Of Activation ◽  
Iron Tricarbonyl ◽  
Proton Chemical Shifts

The circumambulatory rearrangements of some 8,8-dimethylhomotropylium cations and their corresponding iron tricarbonyl complexes have been examined. 8,8-Dimethylhomotropylium cation, 4, has been prepared by protonation of 8,8-dimethyl-bicyclo[5.1.0]octa-3,5-dien-2-ol in FSO3H/SO2ClF. Evidence for homoaromatic delocalization in 4 was found in its characteristic 1H nmr spectrum, particularly when this was compared to that of the non-cyclically delocalized 8,8-dimethyl-bicyclo[5.1.0]octadienyliron tricarbonyl complex 7. Cation 4 was found to be stable at low temperatures but to isomerize to isopropyltropylium ion, 8, at −50 °C, [Formula: see text] The specifically deuterated cation 4D was prepared and a slow circumambulation of C8 around the basal 7-membered ring of this cation was found to occur at −90 °C. The free energy of activation for this circumambulation is 14.5 kcal/mol. Homotropylium cation 4 was also prepared by protonation of 8,8-dimethylbicyclo[3.2.1]octa-3,6-dien-2-ol, 14, at −120 °C. No evidence for the presence of the corresponding bicyclo[3.2.1]octadienyl ion 12 was obtained. The 2,8,8-trimethylhomotropylium cation, 17, was prepared and shown to undergo a circumambulatory rearrangement to give the 4,8,8-trimethyl substituted cation 20 as the major product. In this trimethyl series it also proved possible to generate the 2,8,8-trimethylbicyclo[3.2.1]octadienyl cation, 18, and observe its 1H nmr spectrum at very low temperatures (−116 °C). The proton chemical shifts of 18 suggest that the charge is predominantly located on the 3-carbon bridge. Cation 18 isomerized to 17, 20, and other products at temperatures above −100 °C. The 2,8,8-trimethylbicyclo[5.1.0]octadienyliron tricarbonyl complex 22 was also shown to undergo a circumambulatory rearrangement in which both C8 and the Fe(CO)3 grouping migrate.

Chemical Structures of (+)-Catechin-Formaldehyde Reaction Products (Stiasny Precipitates) Under Strong Acid Conditions: Part 1. Solid-State 13C-NMR Analysis

Holzforschung ◽  
2001 ◽  
Vol 55 (2) ◽  
pp. 205-213 ◽  
Author(s):  
N. Saito ◽  
M. Reilly ◽  
Y. Yazaki
Keyword(s):  
Solid State ◽  
Chemical Shifts ◽  
Strong Acid ◽  
Radiata Pine ◽  
Reaction Products ◽  
Nmr Spectrum ◽  
Chemical Structures ◽  
13C Nmr Analysis ◽  
C Nmr ◽  
Solid State 13C Nmr

Summary To determine more accurately the amount of polyflavanoids in tannin extracts from radiata pine bark, which react with formaldehyde, it is important to elucidate chemical structures of (﹢)-catechin-formaldehyde reaction products (Stiasny precipitates). The Stiasny value of 106.4% for (﹢)-catechin was obtained from the reaction with formaldehyde under strong acid conditions. This value is almost identical to the value calculated from the Stiasny precipitates, which were formed in the ratio of two molecules of (﹢)-catechin to three molecules of formaldehyde. The solid-state 13C NMR spectrum was measured to elucidate the structures of the Stiasny precipitates, and analysed on the basis of the chemical shifts of (﹢)-catechin. The NMR results indicate that C-6 and C-8 in the A-ring are bonded by methylene bridges to form polymers, and also form methylene bridges with C2′, C5′ or C6′ in the B-ring of a catechin unit. Consequently, the reaction products of (﹢)-catechin-formaldehyde under strong acid conditions (Stiasny precipitates) are (﹢)-catechin-polymers, which consist of two moles of (﹢)-catechin and three moles of formaldehyde. The methylene bridges are formed mostly between A-rings, and less frequently, between A- and B-rings and between B-rings of the catechin units.

scholarly journals Tolerance of the Merlo variety population to low temperatures in controlled conditions

2006 ◽  
Vol 51 (1) ◽  
pp. 31-37 ◽  
Author(s):  
Dragan Vujovic ◽  
Radojka Maletic
Keyword(s):  
Cold Storage ◽  
Low Temperatures ◽  
Winter Dormancy ◽  
Controlled Conditions ◽  
Lateral Buds ◽  
Artificial Freezing ◽  
One Year

Tests were carried out on the influence of low temperatures during winter dormancy on per cent of central and lateral buds freezing in Merlot Standard and its varieties. The method applied was in vitro artificial freezing of cuttings of one-year-old shoots in cold storage. Three low temperatures were applied: -15?C, -20?C and -25?C. Tests were performed simultaneously in all varieties three times during winter on December 25, January 25 and February 25 in 1998, 1999 and 2000. The results indicate statistically significant differences between studied varieties and low temperatures applied. Damage of central and lateral buds was significantly lower at -20?C than at -25?C. .

Dimethylhalonium-Ionen in Aluminiumhalogenid/Methylhalogenid-Lösungen / Dimethylhalonium-Ions in Aluminium Halide/Methyl Halide Solutions

1979 ◽  
Vol 34 (7) ◽  
pp. 896-899 ◽  
Author(s):  
Peter Brüggeller ◽  
Erwin Mayer
Keyword(s):  
Time Scale ◽  
Low Temperatures ◽  
Room Temperature ◽  
Chemical Shifts ◽  
Ion Concentration ◽  
Molar Ratio ◽  
Lower Field ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Methyl Halide

Abstract Evidence for the formation of (CH3)2Br+ and (CH3)2I+ in CH3Br and CH3I solutions saturated with AlBr3 comes from the appearance of a second singlet in the 1H NMR spectrum. The (CH3)2Br+ ion is formed at -40 °C to about 5 mol%, the (CH3)2I+ ion at -12 °C with 50 mol% yield. At higher temperatures the concentration of the halonium ions decreases rapidly. The (CH3)2Br+ ion is not detectable at room temperature, the concentration of (CH3)2I+ decreases to about 30 mol%. Dilution of the saturated solutions with methyl halide also reduces the halonium ion concentration. An AlBr3/CH3Br solution with a molar ratio of 1:3 at -40 °C shows no sign of (CH3)2Br+ formation in the XH NMR spectrum. Both effects are best explained by formation of dimethylhalonium ions from the adduct CH3X-AIX3 and by dependence of adduct concentration on temperature and dilution. Exchange of (CH3)2Br+ and (CH3)2I+ with methyl halide is slow on the NMR time scale at low temperatures similar to the results in SbF5/SO2. The 1H NMR singlets of (CH3)2Br+ and (CH3)2I+ are shifted to lower field by 1.32 and 1.68 ppm in comparison with the chemical shifts in SbF5/SO2 solution

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