X‐ray crystal structure,NMR parameters,and conformational study of α‐aminopropanephosphonic acid

X‐ray structural data for α‐aminopropanephosphonic acid (APPA), together with ¹H NMR spectroscopy including PANIC and WIN‐DAISY spectral simulation, and theoretical calculations using the programs VAMP 4.4 (PM3) and GAUSSIAN 92 (3–21G**), confirm an antistaggered relationship between the methyl and phosphonic acid groups in this zwitterionic compound, both in the solid state and in aqueous solution. ³¹P{¹H} and ¹³C{¹H}‐NMR controlled titrations provide information on pK_a values, proton exchange, ion‐specific chemical shifts, and coupling constants in solution. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:314–325, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20609