The Influence of the 2-Alkoxy Group and of C-5 Substituents on the Direction of Reductive Cleavage of 2-Alkoxytetrahydrofurans by AlH2Cl in Ether Solution

1972 ◽  
Vol 50 (10) ◽  
pp. 1502-1512 ◽  
Author(s):  
P. C. Loewen ◽  
Miss L. P. Makhubu ◽  
R. K. Brown
Keyword(s):  
Transition State ◽  
Alkyl Group ◽  
Steric Effect ◽  
Bond Cleavage ◽  
Alkoxy Group ◽  
Ring Cleavage ◽  
Relative Ease ◽  
Ether Solution ◽  
A Minor ◽  
Minor Extent

The AlH2Cl hydrogenolysis of ether solutions of 2-alkoxytetrahydrofurans in which the alkoxy group is either CH3O, C2H5O, i-C3H7O, or t-C4H9O, gives only those products resulting from ring C—O bond cleavage. However, substituents at C-5 of 2-methoxytetrahydrofuran exert a strong effect on the ratio of ring to exo C—O bond cleavage. Thus, alkyl (electron donor) groups at C-5 promote an increase in the amount of exo cleavage, the proportion increasing from 62.5 to 100% as the C-5 alkyl group is changed from CH3 to t-C4H9. In contrast, electron withdrawing substituents, CH3OCH2— and C6H5, at C-5 favor ring cleavage to the extent of 93 and 84% respectively.The results are interpreted in terms of the influence that these substituents exert through their electronic properties on the relative ease of attainment of the transition state leading to either ring C—O or exo C—O bond cleavage. However, evidence is provided to show that the bulk steric effect of these substituents also controls, though to a minor extent, the proportion of ring to exo cleavage.

Metal-Metal Cooperative Bond Activation by Heterobimetallic Alkyl, Aryl, and Acetylide PtII/CuI Complexes

2020 ◽  
Author(s):  
Shubham Deolka ◽  
Orestes Rivada Wheelaghan ◽  
Sandra Aristizábal ◽  
Robert Fayzullin ◽  
Shrinwantu Pal ◽  
...  
Keyword(s):  
Alkyl Group ◽  
Bond Activation ◽  
Bond Cleavage ◽  
Terminal Alkyne ◽  
Alkyl Aryl ◽  
Metal Metal ◽  
The Stability ◽  
Selective Formation ◽  
Organoplatinum Compounds

We report selective formation of heterobimetallic PtII/CuI complexes that demonstrate how facile bond activation processes can be achieved by altering reactivity of common organoplatinum compounds through their interaction with another metal center. The interaction of the Cu center with Pt center and with a Pt-bound alkyl group increases the stability of PtMe2 towards undesired rollover cyclometalation. The presence of the CuI center also enables facile transmetalation from electron-deficient tetraarylborate [B(ArF)4]- anion and mild C-H bond cleavage of a terminal alkyne, which was not observed in the absence of an electrophilic Cu center. The DFT study indicates that the role of Cu center acts as a binding site for alkyne substrate, while activating its terminal C-H bond.

Nitro–Nitrite Isomerization and Transition State Switching in the Dissociation of Ionized Nitromethane: A Threshold Photoelectron–Photoion Coincidence Spectroscopy Study

2009 ◽  
Vol 15 (2) ◽  
pp. 157-166 ◽  
Author(s):  
Brandon Ferrier ◽  
Anne-Marie Boulanger ◽  
David M.P. Holland ◽  
David A. Shaw ◽  
Paul M. Mayer
Keyword(s):  
Transition State ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Bond Cleavage ◽  
Cleavage Reaction ◽  
Nitrite Ion ◽  
Methyl Nitrite ◽  
Bond Cleavage Reaction ◽  
Entropy Of Activation ◽  
Lower Entropy

Threshold photoelectron–photoion coincidence (TPEPICO) spectroscopy has been employed to investigate the competition between bond cleavage and rearrangement reactions in the dissociation of ionized nitromethane, 1. Modeling TPEPICO breakdown diagrams with a combination of RRKM theory and ab initio calculations at the G3 level of theory allowed the derivation of the activation energy for the isomerisation of 1 to ionized methyl nitrite, 2, 82 kJ mol−1. In addition, evidence was found for a transition state switch in the bond cleavage reaction in 1 leading to CH3• + NO2+. As internal energy increases, the effective transition state for this reaction becomes tighter (i.e. is characterized by a lower entropy of activation, Δ‡S). Fitted thresholds for NO+ and CH2OHO+ ions, originating from the isomeric methyl nitrite ion, are consistent with G3 level ab initio calculations.

Factors affecting the future of the Scottish hydrometric network

1987 ◽  
Vol 78 (4) ◽  
pp. 269-274 ◽  
Author(s):  
T. Poodle
Keyword(s):  
Data Acquisition ◽  
Computer Systems ◽  
Economic Recession ◽  
Data Standards ◽  
Factors Affecting ◽  
Economic Climate ◽  
A Minor ◽  
The Cost ◽  
Minor Extent

ABSTRACTThe Scottish Hydrometric Network consists of a number of river gauging stations which have been located at sites considered suitable to provide long term flow records. Economic recession has placed some stress on the gauging programme, and has given rise to extensive closures of gauging stations in England and, to a minor extent so far, in Scotland. The way in which the network became established provides a mixture of strengths and weaknesses which could have unpredictable consequences in an adverse economic climate. Changing technology provides some opportunity to reduce the cost of data acquisition and improve the deployment of manpower, while maintaining data standards. In these changing circumstances, particularly with extensive use of computer systems, it is important that standards are established for data returned to the Water Archive and that the network is not allowed to degenerate by default.

Cupressus arizonica (Arizona cypress).

2021 ◽  
Author(s):  
Sylvan Kaufman
Keyword(s):  
New World ◽  
Erosion Control ◽  
Economic Importance ◽  
Christmas Trees ◽  
Cupressus Arizonica ◽  
A Minor ◽  
Minor Extent

Abstract At present, in the New World, C. arizonica and its varieties are of low economic importance, but they are sometimes cut for fenceposts, fuelwood and lumber, and recently they have become popular as Christmas trees. By contrast, the Arizona cypress (C. arizonica var. arizonica) and the smooth cypress (C. arizonica var. glabra) are widespread in Europe and are used for landscaping, erosion control, windbreaks, and to a minor extent for lumber.

Chapter II. The World Economy

1983 ◽  
Vol 106 ◽  
pp. 26-38
Keyword(s):  
North America ◽  
Industrial Production ◽  
World Economy ◽  
Western Europe ◽  
West Germany ◽  
The Us ◽  
The World ◽  
The Uk ◽  
A Minor ◽  
Minor Extent

The recovery in the OECD area gathered pace in the second quarter, when its total GDP probably increased by as much as 1 per cent. The rise was, however, heavily concentrated in North America and particularly the US. There may well have been a slight fall in Western Europe, where the level of industrial production hardly changed and increases in gross product in West Germany and, to a minor extent, in France were outweighed by falls in Italy and (according to the expenditure measure) the UK.

scholarly journals Tracing the (hidden) spatialities of digital agendas: the case of ‘Digital Hungary’

2019 ◽  
Vol 26 (2) ◽  
pp. 135-150
Author(s):  
Krisztina Varró
Keyword(s):  
Analytical Framework ◽  
Spatial Dimension ◽  
Spatial Development ◽  
Digital Transformation ◽  
A Minor ◽  
Development Trajectories ◽  
Minor Extent

Policies that aim at bringing about a digital transformation (seek to) create the conditions for particular spatial development trajectories. Yet, the understandings, explicit and implicit, of space advanced by digital agendas have remained rather underexposed to date. This paper addresses this gap by developing a Foucauldian-inspired discourse-analytical framework and applies it to the programme of ‘Digital Hungary’. It is argued that policies of digitalisation in Hungary only to a minor extent consider the spatial dimension, and their impact potentially undermines the declared aims of spatial development at different scales.

scholarly journals Bryophytes of the upper reaches of the Western Bug River (Lviv Region, Ukraine)

2020 ◽  
pp. 7-24
Author(s):  
Yura Drach ◽  
Zvenysvala Mamchur
Keyword(s):  
Development Strategy ◽  
Life Forms ◽  
Wetland Ecosystems ◽  
Substrate Preferences ◽  
Ecological Features ◽  
The Development Strategy ◽  
Cold Tolerant ◽  
A Minor ◽  
First Time ◽  
Minor Extent

In the article, the bryophytes of the upper reaches of the Western Bug River, which is physically and geographically located within Male Polissya, partly Roztochia, and to a minor extent in the Gologoro-Voronyatsky denudo-structural hills, have been studied. Based on our survey, a list of the bryophytes has been compiled for the first time. Ecological features, substrate preferences and life forms of the bryophytes have been analysed. According to the ecological features, subheliophytes (30.9%) and hemisciophytes (30.9%) predominate in the spectrum of heliomorphs; mesophytes (29.7%), hygromesophytes (21.2%) and xeromesophytes – in the spectrum of hydromorphs (19.4%); cold-tolerant species (59.4%) – in the spectrum of thermomorphs. Based on the analysis of the substrate preferences of the bryophytes, the following groups were identified: epigeans (116 species), epixils (56 species), epiphytes (46 species), epiliths (43 species), aquatic (22 species). The prevailing life forms are turf (30.3%), rough mat (18.2%), weft (15.2%), tuft (10.3%) and smooth mat (9.7%). 3 species that are officially recognised as rare and 16 species that are recognized as regionally rare have been found. In the group of bryophytes associated with wetland ecosystems, 2 officially rare and 6 regionally rare species were found in the study area. Given the large areas of drained land in Lviv Region, these species are of particular value, especially in the context of conservation of the biodiversity and protection of the valuable natural areas in accordance with the Development Strategy of Lviv Region by 2027.

scholarly journals Gender in modern Greek historiography

HISTOREIN ◽  
2017 ◽  
Vol 16 (1-2) ◽  
pp. 74
Author(s):  
Nikolaos Papadogiannis
Keyword(s):  
Gender Relations ◽  
Historical Research ◽  
International Level ◽  
Systematic Analysis ◽  
Modern Greek ◽  
Gender And Age ◽  
Greek Historiography ◽  
Gender Factor ◽  
A Minor ◽  
Minor Extent

This article analyses the emergence and development of the study of gender in modern Greek historiography in the broader sense, exploring works that incorporate, even to a minor extent, the gender factor. It shows that despite the manifold barriers that gender historians have faced, there has been a slow but steady process of diffusion of gender in modern Greek historiography in general. The article also shows that historical research on gender relations in Greece initially focused on the study of women, historicising, however, their relations with men. Thus, in line with what Kantsa and Papataxiarchis argue about the relevant scholarship at the international level, no linear transition from the study of women to the examination of gender relations occurred. What has transpired in the last two decades, however, is that the relevant historiography has gradually broadened to encompass a more systematic analysis of the (re)making of masculinities. It has also been enriched by the study of the intersection of gender and age as well as of transnational flows and their impact on gender, tendencies that have been slightly neglected in other reviews of the study of gender in Greek historiography. 

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