Tt-n interaction

Taking this approach a step further, the same group developed a system that used Tt—n interactions as well as hydrogen bonds, in which the pyrene units were attached at the ends of a polybutadiene polymer that was functionalized with urethane groups. The blend showed an increased tensile modulus compared to... 

The brush-type (Pirkle-type) CSPs have been used predominantly under normal phase conditions in LC. The chiral selector typically incorporates tt-acidic and/or n-basic functionality, and the chiral interactions between the analyte and the CSP include dipole-dipole interactions, n-n interactions, hydrogen bonding, and steric hindrance. The concept of reciprocity has been used to facilitate the rational design of chiral selectors having the desired selectivity [45]. 

The unsymmetric n face of carbonyl groups is postulated to be attributable to orbital interactions between a o-fragment and a tt-fragment. Interactions between two 7t fragments in a carbonyl molecule can also lead to an unsymmetrical orbital phase environment [3]. 

CH" 7t bonds work cooperatively. The weak directionality of CH-tt interactions and the large surfaces offered by n systems means that many aromatic compounds exhibit multiple such interactions. While they are individually weak their combined, cooperative effect can be very significant. The existence of CH-n interactions is manifest in the commonly higher melting points and facile crystallisation of aromatic compounds compared to aliphatic compounds of similar molecular weight. 

Fig. 2. Solid-state structure of the PhC(0)N Pr2 B(C6F5)3 adduct, illustrating the tt stacking interaction.

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