Cyclophanes. XII* The Synthesis of [2,2](3,3')Biphenylo(3,6)-phenanthrenophanes and Attempted Conversions into Hepta[8]circulene

1979 ◽  
Vol 32 (2) ◽  
pp. 361 ◽  
Author(s):  
DN Leach ◽  
JA Reiss
Keyword(s):  
Ring Contraction ◽  
Factors Affecting ◽  
Spectral Evidence ◽  
Saturated Compound ◽  
Contraction Procedure

[2,2](3,3')Biphenylo(3,6)phenanthrenophane-1,15-diene (6) has been synthesized by a ring-contraction procedure from the dithiacyclophane (10). The corresponding saturated compound (5) was prepared by pyrolysis of the sulfone (12). The stereochemistry of both (5) and (6) in solution has been determined to be syn from spectral evidence and neither compound shows any evidence of conformational ring-flipping or extensive mobility. Several attempts to convert the diene (6) into hepta[8]circulene are recorded. The factors affecting the photochemical ring-closures of cyclophanedienes are discussed.

Cyclophanes. VI. The synthesis of [2,2](3,3')biphenylparacyclophanedienes

1976 ◽  
Vol 29 (6) ◽  
pp. 1267 ◽  
Author(s):  
PJ Jessup ◽  
JA Reiss
Keyword(s):  
Ring Opening ◽  
Ring System ◽  
Ring Contraction ◽  
Stevens Rearrangement ◽  
Ring Opening Reaction ◽  
Disubstituted Benzene ◽  
Contraction Procedure

The preparations of [2,2](3,3')biphenylparacyclophane-1,9-dine (19) and a dimethyl derivative (20) synthesized by a ring-contraction procedure of the corresponding dithiacyclophanes (11) and (12) are reported. Both dienes (19) and (20) photocyclized under oxidative conditions to the benzo[ghi]- perylenes (21) and (22). Difficulties associated with the Stevens rearrangement in cyclophanes containing a para-disubstituted benzene moiety have been rationalized in terms of a competing ring- opening reaction. Several other reactions of the biphenylparacylophane ring system are reported, and the stereochemistry of the macrocycle is discussed.

The C7H6 energy surface: phenylcarbene and 2-Methylene-3,5-cyclohexadienylidene - A duality of mechanism

1973 ◽  
Vol 26 (8) ◽  
pp. 1705 ◽  
Author(s):  
WD Crow ◽  
MN Paddon-Row
Keyword(s):  
Gas Phase ◽  
Energy Surface ◽  
Ring Contraction ◽  
Factors Affecting ◽  
Tracer Techniques ◽  
13C Tracer

The conversion of phenylcarbene (1) into fulvenallene (17) and ethynylcyclo-pentadiene (18) on gas-phase pyrolysis has been examined by 13C-tracer techniques. Complete randomization of all seven carbon atoms has been shown to precede ring contraction. The result is consistent with a pool of intermediates [cycloheptatrienylidene (19) and bicyclo[4,1,0]hepta-2,4,6-triene (21)], interconverting rapidly through tautomerism and concomitant H-shifts. Dimerization, intramolecular trapping, and ring contraction constitute the major exits from this pool. ��� Gas-phase thermolysis of indazole generates the same products (17)/(18) and in this case the mechanism has been investigated by the intramolecular trapping in 1-deutero-3-methylindazole to yield deuterostyrenes. Two pathways are revealed, proceeding respectively through phenylcarbene and 2-methylene-3,5-cyclohexadienyl-idene (36); factors affecting the latter pathway are discussed.

Progress In The Practical Application Of Automated Image Analysis To Tem Negatives

1977 ◽  
Vol 35 ◽  
pp. 214-217
Author(s):  
F. A. Heckman ◽  
E. Redman ◽  
J.E. Connolly
Keyword(s):  
Image Analysis ◽  
Image Quality ◽  
Exposure Time ◽  
Image Contrast ◽  
Automated Image Analysis ◽  
Practical Application ◽  
Factors Affecting ◽  
High Image Quality ◽  
Qualitative Evidence ◽  
Comprehensive Study

In our initial publication on this subject1) we reported results demonstrating that contrast is the most important factor in producing the high image quality required for reliable image analysis. We also listed the factors which enhance contrast in order of the experimentally determined magnitude of their effect. The two most powerful factors affecting image contrast attainable with sheet film are beam intensity and KV. At that time we had only qualitative evidence for the ranking of enhancing factors. Later we carried out the densitometric measurements which led to the results outlined below.Meaningful evaluations of the cause-effect relationships among the considerable number of variables in preparing EM negatives depend on doing things in a systematic way, varying only one parameter at a time. Unless otherwise noted, we adhered to the following procedure evolved during our comprehensive study:Philips EM-300; 30μ objective aperature; magnification 7000- 12000X, exposure time 1 second, anti-contamination device operating.

Factors affecting microstructural scale in liquid crystalline polymers

1990 ◽  
Vol 48 (4) ◽  
pp. 220-221
Author(s):  
Christine M. Dannels ◽  
Christopher Viney
Keyword(s):  
Liquid Crystalline ◽  
Liquid Crystalline Polymers ◽  
Factors Affecting ◽  
Crystalline Polymers ◽  
Thermal Expansion Coefficients ◽  
Low Thermal Expansion ◽  
Lower Viscosity ◽  
Fine Microstructure ◽  
Planar Orientation ◽  
Strength And Stiffness

Processing polymers from the liquid crystalline state offers several advantages compared to processing from conventional fluids. These include: better axial strength and stiffness in fibers, better planar orientation in films, lower viscosity during processing, low solidification shrinkage of injection moldings (thermotropic processing), and low thermal expansion coefficients. However, the compressive strength of the solid is disappointing. Previous efforts to improve this property have focussed on synthesizing stiffer molecules. The effect of microstructural scale has been overlooked, even though its relevance to the mechanical and physical properties of more traditional materials is well established. By analogy with the behavior of metals and ceramics, one would expect a fine microstructure (i..e. a high density of orientational defects) to be desirable.Also, because much microstructural detail in liquid crystalline polymers occurs on a scale close to the wavelength of light, light is scattered on passing through these materials.

Factors affecting dentist participation in a state Medicaid program

1990 ◽  
Vol 54 (11) ◽  
pp. 638-643 ◽  
Author(s):  
PC Damiano ◽  
ER Brown ◽  
JD Johnson ◽  
JP Scheetz
Keyword(s):  
Medicaid Program ◽  
Factors Affecting

Speech Therapy Services in a Large School System: A Six-Year Overview

1976 ◽  
Vol 7 (4) ◽  
pp. 207-219 ◽  
Author(s):  
Constance P. DesRoches
Keyword(s):  
School System ◽  
Speech Therapy ◽  
Factors Affecting ◽  
Case Load ◽  
Number Of Children ◽  
School Population ◽  
System A ◽  
Therapy Services ◽  
And Shifts ◽  
Selection Factors

A statistical review provides analysis of four years of speech therapy services of a suburban school system which can be used for comparison with other school system programs. Included are data on the percentages of the school population enrolled in therapy, the categories of disabilities and the number of children in each category, the sex and grade-level distribution of those in therapy, and shifts in case-load selection. Factors affecting changes in case-load profiles are identified and discussed.

Assessing the Link Between Perception and Production in Cantonese Tone Acquisition

2019 ◽  
Vol 62 (5) ◽  
pp. 1243-1257 ◽  
Author(s):  
Peggy Pik Ki Mok ◽  
Holly Sze Ho Fung ◽  
Vivian Guo Li
Keyword(s):  
Language Acquisition ◽  
General Principle ◽  
Choice Task ◽  
Factors Affecting ◽  
Tone Pair ◽  
Tone Production ◽  
Monosyllabic Words ◽  
Early Production ◽  
Forced Choice Task ◽  
Production Accuracy

Purpose Previous studies showed early production precedes late perception in Cantonese tone acquisition, contrary to the general principle that perception precedes production in child language. How tone production and perception are linked in 1st language acquisition remains largely unknown. Our study revisited the acquisition of tone in Cantonese-speaking children, exploring the possible link between production and perception in 1st language acquisition. Method One hundred eleven Cantonese-speaking children aged between 2;0 and 6;0 (years;months) and 10 adolescent reference speakers participated in tone production and perception experiments. Production materials with 30 monosyllabic words were transcribed in filtered and unfiltered conditions by 2 native judges. Perception accuracy was based on a 2-alternative forced-choice task with pictures covering all possible tone pair contrasts. Results Children's accuracy of production and perception of all the 6 Cantonese tones was still not adultlike by age 6;0. Both production and perception accuracies matured with age. A weak positive link was found between the 2 accuracies. Mother's native language contributed to children's production accuracy. Conclusions Our findings show that production and perception abilities are associated in tone acquisition. Further study is needed to explore factors affecting production accuracy in children. Supplemental Material https://doi.org/10.23641/asha.7960826

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