Effect of Single-Walled Carbon Nanotube Association upon Representative Amides

Abstract

Select amides have been widely used to suspend nanoarchitectures in organic solvents. In order to determine factors enabling these suspensions, interactions of single-walled carbon nanotubes (SWCNTs) with representative amides 1 were examined—R(C═O)NMe2, when R = H, Me, Et, i-Pr, t-Bu, Ph. 1H NMR spectra gave evidence for two types of SWCNT: amide associations, formed after evaporation of the reaction mixture to either a concentrated solution or a wet paste, followed by sonication in NMR solvent. NMR spectra of SWCNTs associated with 1 (SWCNT:1) after evaporation to concentrated solution show broadening and small downfield changes, suggesting weak interactions. Evaporation of SWCNT:1 to a wet paste causes larger spectral changes, predominantly in aldehydic and α proton signals. These are often 10 times those in concentrated solution, especially when R has small steric requirements, which suggests a stronger interaction of 1 with SWCNTs under wet paste conditions. 1H NMR signal changes of 1, which accompany SWCNT:1 association, depend upon (1) degree of evaporation of residual amide and organic solvent, (2) organic and NMR solvent combination, (3) type of proton in R, (4) proximity effects to the carbonyl (R versus NMe2), and (5) steric requirements of R.