S1 Supporting Information for Hydrogen-Bond Symmetry in Difluoromaleate Monoanion Charles L. Perrin,* Phaneendrasai Karri, Curtis Moore, and Arnold L. Rheingold Department of Chemistry, University of California San Diego La Jolla, CA 92093-0358 USA cperrin@ucsd.edu Instrumentation. Mass spectra were obtained using Q-TOF/MS, with ESI in negative ion mode. NMR spectra were recorded on a JEOL-500 FT-NMR spectrometer (470 MHz 19 F) with 2H lock, except for liquid crystal solvents. The probe was double tuned to 1 H and 19 F, and a 7.0-s 45º pulse width was used. Spectra used spectral widths of 80-400 ppm with 32K to 64K data points and zero-filled 4 times. The spectra were recorded with sample spinning at 18 Hz, and the temperature was controlled at 291 K (328 K for liquid crystal). Diffraction Techniques. Single-crystal X-ray diffraction studies were carried out on a Bruker Kappa APEXII CCD diffractometer equipped with Cu K! radiation (" = 1.5478Å). The crystals were affixed to a Nylon cryoloop using oil (Paratone-n, Exxon) and mounted in the cold stream of the diffractometer. The temperature at the crystal was maintained at 120 K using a Cryostream 700EX cooler (Oxford Cryosystems). Data collection, reduction, structure solution, and refinement were performed using the Bruker Apex2 suite. All available reflections to 2# max were harvested and corrected for Lorentz and polarization factors with Bruker SAINT. Reflections were then corrected for absorption, interframe scaling, and other systematic errors with SADABS 2008/1. The structure was solved (direct methods) and refined (full-matrix least-squares against F 2 ) with the Bruker SHELXTL package. All non-hydrogen atoms were fully refined using anisotropic thermal parameters. The hydrogen of the intramolecular hydrogen bond was fully refined using isotropic thermal parameters. Materials. 1,1,2-Trichloro-2,3,3-trifluorocyclobutane and tetrabutylammonium hydroxide (1 M aqueous) were purchased from Aldrich Chemical Company. Trifluorosuccinic acid was
S2 purchased from Ryan Scientific. 4-Cyanophenyl 4-heptylbenzoate was purchased from Acros Organics. H 2 18 O in 1 ml ampoules (97.6 atom% 18 O) was obtained from Isotec Labs. NMR solvents D 2 O, CD 3 CN, and CD 2 Cl 2 were purchased from Cambridge Isotope Labs. Difluoromaleic + difluorofumaric acids. A mixture of 2 ml of water, 0.48 g (12 mmol) of sodium hydroxide and 0.688 g (4 mmol) of trifluorosuccinic acid was heated on a steam bath for 15 h. The mixture was cooled and 1.6 ml of sulfuric acid diluted with 1 ml of water was added. The solution was extracted with ether and the ether solution was decolorized with carbon, dried, and evaporated to give 0.512 g (74% yield) of a mixture of difluorofumaric acid and difluoromaleic acids. Difluoromaleic anhydride. A mixture of difluoromaleic and difluorofumaric acids (0.4 g., 2.61 mmol) and phosphorus pentoxide (0.4 g., 2.77 mmol) in a 5-mL round bottom flask was heated at 100 ºC for 30 min. The difluoromaleic anhydride was distilled under reduced pressure to give 0.19 g (54% yield), b.p. 40 ºC/ 25 mmhg (lit 1 b.p. 128). Difluoromaleic acid. Difluoromaleic anhydride was hydrolyzed with water in the presence of a small amount of tetrahydrofuran. The solvent was evaporated and the residue was recrystallized from a mixture of acetone and benzene. The acid melted at 214-218 ºC (lit. 219-20). Hydrolysis in H 2 18 O produced an acid whose mass pectrum is shown in Fig. S1. Difluoromaleic acid could also be obtained from the dianion by acidification with 20% H 2 SO 4 and rapid extraction into ether, but this procedure washes some 18 O out of the acid. Sample Preparation. Samples were prepared as 0.1-0.2 M solutions in D 2 O, with NaBF 4 as internal standard and a trace of Na 2 EDTA. The samples were deoxygenated with sonication under vacuum. Titration of unlabeled acid served to measure 19 F chemical shifts of diacid, monoanion, and dianion. Then 19 F chemical shifts and the 18 O-induced isotope shifts were measured for the labeled acid after addition of each equivalent of 1.0 M KOH. The final sample was reacidified with 20% H 2 SO 4 to a ph near zero to obtain diacid shifts. NMR Spectra. The 19 F NMR spectrum of mono- 18 O-labeled difluoromaleate dianion in 1. Raasch, M. S.; Miegel, R. E.; Castle, J. E. J. Am. Chem. Soc. 1959, 81, 2678.
S3 D 2 O is shown in Fig. S2. The 19 F NMR spectrum of 1:2 mixture of unlabeled and mono- 18 O- labeled difluoromaleate monoanion (3 + 3-18 O) in D 2 O is shown in Fig. S3. The 19 F NMR spectrum of the tetrabutylammonium salt of a 1:2 mixture of unlabeled and mono- 18 O-labeled difluoromaleate monoanion (3 + 3-18 O) in CD 2 Cl 2 is shown in Fig. S4. Figure S1. Mass spectrum of the diacid isolated from reaction of difluoromaleic anhydride (2) with H 2 18 O.
Figure S2. 19 F NMR spectrum of mono- 18 O-labeled difluoromaleate dianion (4-18 O) in D 2 O. S4
S5 Figure S3. 19 F NMR spectrum of a 1:2 mixture of unlabeled and mono- 18 O-labeled difluoromaleate monoanion (3 + 3-18 O) in D 2 O.
S6 Figure S4. 19 F NMR spectrum of the tetrabutylammonium salt of a 1:2 mixture of unlabeled and mono- 18 O-labeled difluoromaleate monoanion (3 + 3-18 O) in CD 2 Cl 2.
S7 Figure S5. Simulated 19 F NMR spectrum of a 1:2 mixture of unlabeled and mono- 18 O-labeled difluoromaleate monoanion (3 + 3-18 O) in CD 2 Cl 2, as in Fig. S4, but with 6 Hz additional line broadening.
S8 Table S1. Crystallographic data for potassium hydrogen difluoromaleate (K + 3). Formula C 4 HF 2 KO 4 K + 3 a, Å 4.6377 d O-O 2.412 b, Å 8.0574 d O-H 1.206 c, Å 15.4299 d O-H' 1.206!, deg 90.00 d C=O 1.218 $, deg 90.00 d C-OH 1.295 %, deg 90.00 d FC=CF 1.333 V, Å 3 576.58 d C-CO 1.488 Z 4 & O-H-O 177.18 fw 190.15 & F-C=CF 116.55 space group Pbcm & O2C-C=CCO2 131.88 T, K 120 & F-C-CO2 b 111.56 ", Å 1.54178 ' F-C=C-F 0.00 d, mg m -3 2.190 ' O2C-C=C-CO2 0.00 µ, mm -1 8.306 ' F-C=C-CO2 179.63 R(F o ), all data 0.1268 ' O=C-C=CCO2 0.00 ' O-C-C=CCO2 4.92 ' H-O-C-O 175.64 ' H-O-C-C 4.86 Bond lengths (d, Å), bond angles (&, deg), and torsional angles (', deg)