Temperature dependence of proton chemical shifts of aqueous sodium fluoride, sodium hydroxide, and tetramethylammonium hydroxide: the internal tetramethylammonium ion standard

Abstract

Proton chemical shifts have been determined over a range of temperature for water, and for aqueous sodium fluoride and sodium or tetramethylammonium hydroxide solutions using Me₄N⁺ as an internal standard. The water results agree closely with those of Hindman and confirm that the shift temperature dependence is not constant over the range 0–100 °C. The shifts of NaF solutions can be explained by including a downfield shift increment arising from the electric field of the fluoride ion; the latter is the only unicharged anion for which such an effect has been detected. The absolute shift of the hydroxide ion was estimated from the results assuming it introduces the same low-field increment in its co-ordinated water. It is 14·2 p.p.m. low field of C₂H₆ and is probably slightly less descreened than H₃O⁺. The presence of ion-pairing in sodium hydroxide solutions is confirmed.