Structural Factors That Influence Base Strength

4 STRUCTURAL FACTORS THAT INFLUENCE BASE STRENGTH 

1 Anions Are More Basic than the Corresponding Neutrai Species 

Anions are more electron rich and so are more basic as illustrated by the higher p/sTabH of the anions compared to their neutrals in the following compounds. 

2 Lone Pairs with Less s Character are More Basic 

Keeping within the same atom, mixing more s orbital into the lone pair hybridization stabilizes the lone pair because a 2s orbital is lower in energy than a 2p orbital. The more stable lone pair is less basic and harder to protonate illustrated by the lower pKabH of the following compounds. Sections 3.4.4 to 3.4.6 are exceptions to this and to the next trend. 

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Section 3.4 Structural Factors That Influence Base Strength 71... 

Structural features are not the only factors that affect acidity or basicity. The same compound can have its acidity or basicity changed when the conditions are changed. The effect of temperature (p. 364) has already been mentioned. More important is the effect of the solvent, which can exert considerable influence on acid and base strengths by differential solvation. If a base is more solvated than its conjugate acid, its stability is increased relative to the conjugate acid. For example,... 

Apparently, dispersed fibres do not appreciably modify the behaviour of cement-based elements subjected to creep. There have been few experimental studies of this problem and the results obtained are inconclusive. As mentioned above for shrinkage, modification of the internal structure of composite materials causes quite complex results and comparisons are difficult. In several reports, similar behaviour of plain and fibre-reinforced elements was observed under creep conditions, both qualitatively and quantitatively. However, extensive studies executed by Swamy et al. (1977) proved that fibre-reinforcement decreased creep considerably. Similar conclusions were formulated by Brandt and Hebda (1989) who tested elements under eccentric compression in long periods of time. The creep was small for reinforced specimens. The most important factor relating to the final creep values was the level of load with respect to the material s strength and that factor was also influenced by the volume of fibre reinforcement. That was the reason why the creep recovery measurements carried out by different authors did not furnish consistent results. 

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