The different degrees of lone-pair overlap ought also to be reflected in the basicity of the nitrogen. Compounds 7 are poorly water soluble, and determination of pK a values in nonaqueous solvents is non-trivial. We recently developed an NMR-based assay using pH gradients in a single sample and chemical shift imaging to determine pK a values in DMSO. 20,21 Using this method, a significant variation in pK a was observed: over 3 units separate the three compounds 7a,b,d in the homologous series, with the most strained variant 7a being the most basic as expected. This trend in relative basicity was also confirmed computationally in water using the Jaguar pK a prediction method.