Despite the prevalence of alcohols and carboxylic acids as functional groups in organic molecules and the potential to serve as radical precursors, C−O bonds remain difficult to activate. We report a synthetic strategy for direct access to both alkyl and acyl radicals from these ubiquitous functional groups via photoredox catalysis. This method exploits the unique reactivity of phosphoranyl radicals, generated from a polar/SET crossover between a phosphine radical cation and an oxygen-centered nucleophile. We show the desired reactivity in the reduction of benzylic alcohols to the corresponding benzyl radicals with terminal H atom trapping to afford the deoxygenated products. Using the same method, we demonstrate access to synthetically versatile acyl radicals, which enables the reduction of aromatic and aliphatic carboxylic acids to the corresponding aldehydes with exceptional chemoselectivity. This protocol also transforms carboxylic acids to heterocycles and cyclic ketones via intramolecular acyl radical cyclizations to forge C−O, C−N, and C−C bonds in a single step.

We have recently developed vetted methods for obtaining quantitative infrared directional-hemispherical reflectance spectra using a commercial integrating sphere. In this paper, the effects of particle size on the spectral properties are analyzed for several samples such as ammonium sulfate, calcium carbonate, and sodium sulfate as well as one organic compound, lactose. We prepared multiple size fractions for each sample and confirmed the mean sizes using optical microscopy. Most species displayed a wide range of spectral behavior depending on the mean particle size. General trends of reflectance versus particle size are observed such as increased albedo for smaller particles: for most wavelengths, the reflectivity drops with increased size, sometimes displaying a factor of 4 or more drop in reflectivity along with a loss of spectral contrast. In the longwave infrared, several species with symmetric anions or cations exhibited reststrahlen features whose amplitude was nearly invariant with particle size, at least for intermediate and large size sample fractions: that is, ≳150  μm. Trends of other types of bands (Christiansen minima, transparency features) are also investigated as well as quantitative analysis of the observed relationship between reflectance versus particle diameter.

I. General Information Materials. Commercial reagents were acquired from Sigma-Aldrich, Alfa Aesar, Acros, Strem, TCI, or Oakwood and used as received. Diethyl ether (Et2O), tetrahydrofuran (THF), and toluene (PhMe) were dried by passing through activated alumina columns and stored over molecular sieves in a N2-filled glovebox; N,N-dimethylformamide (DMF) was dried by passing through a column of activated molecular sieves. Acetonitrile (MeCN) was purchased from Millipore Sigma without sieves and subsequently sparged with nitrogen before bringing it into the glovebox. Sieves were detrimental for reactivity. Instrumentation. Proton nuclear magnetic resonance (1 H NMR) spectra were recorded on a Bruker 500 AVANCE spectrometer (500 MHz), a Bruker NB 300 spectrometer (300 MHz), or a Bruker Avance III HD NanoBay (400 MHz) spectrometer. Deuterium nuclear magnetic resonance (2 H NMR) spectra were recorded on a Bruker 500 AVANCE spectrometer (77 MHz). Carbon nuclear magnetic resonance (13 C NMR) spectra were recorded on a Bruker 500 AVANCE spectrometer (126 MHz). Fluorine nuclear magnetic resonance (19 F NMR) spectra were recorded on a Bruker NB 300 spectrometer (282 MHz). Chemical shifts for protons are reported in parts per million (ppm) downfield from tetramethylsilane and are referenced to residual protium in the NMR solvent (CHCl3 =  7.26 ppm). Chemical shifts for carbon are reported in parts per million downfield from tetramethylsilane and are referenced to the carbon resonances of the solvent residual peak (CDCl3 =  77.16 ppm). Chemical shifts for fluorine are reported in parts per million referenced to CFCl3 ( 0 ppm). NMR data are represented as follows: chemical shift ( ppm), multiplicity (s = singlet, bs = broad singlet, d = doublet, appd = apparent doublet, t = triplet, q = quartet, p = pentet, sx = sextet m = multiplet), coupling constant in Hertz (Hz), integration. Reversed-phase liquid chromatography/mass spectrometry (LC/MS) was performed on an Agilent 1260 Infinity analytical LC and Agilent 6120 Quadrupole LC/MS system, using electrospray ionization/atmospheric-pressure chemical ionization (ESI/APCI), and UV detection at 254 and 280 nm. High-resolution mass spectra were obtained on an Agilent 6220 LC/MS using electrospray ionization time-of-flight (ESI-TOF) or Agilent 7200 gas chromatography/mass spectrometry using electron impact time-of-flight (EI-TOF). Gas chromatography was performed on an Agilent 7890A series instrument equipped with a split-mode capillary injection system and flame ionization detectors. Fourier transform infrared (FT-IR) spectra were recorded on a Perkin-Elmer Spectrum 100 and are reported in terms of frequency of absorption (cm-1). High-performance liquid chromatography (HPLC) was performed on an Agilent 1200 series instrument with a binary pump and a diode array detector, using Chiralcel OD-H (25 cm x 0.46 cm), Chiralcel OJ-H (25 cm x 0.46 cm), Chiralpak ASH (25 cm x 0.46 cm), Chiralpak AD-H (25 cm x 0.46 cm), Chiralpak IC (25 cm x 0.46 cm) and Chiralpack ID (25 cm x 0.46 cm). ...

Alcohols and carboxylic acids are ubiquitous functional groups found in organic molecules that could serve as radical precursors, but C–O bonds remain difficult to activate. We report a synthetic strategy for direct access to both alkyl and acyl radicals from these ubiquitous functional groups via photoredox catalysis. This method exploits the unique reactivity of phosphoranyl radicals, generated from a polar/SET crossover between a phosphine radical cation and an oxygen centered nucleophile. We first show the desired reactivity in the reduction of benzylic alcohols to the corresponding benzyl radicals with terminal H-atom trapping to afford the deoxygenated product. Using the same method, we demonstrate access to synthetically versatile acyl radicals which enables the reduction of aromatic and aliphatic carboxylic acids to the corresponding aldehydes with exceptional chemoselectivity. This protocol also transforms carboxylic acids to heterocycles and cyclic ketones via intramolecular acyl radical cyclizations to forge new C–O, C–N and C–C bonds in a single step.

For geologic and extraterrestrial samples it is known that both particle size and morphology can have strong effects on a species' infrared reflectance spectra. Due to such effects, the reflectance spectra cannot be predicted from the absorption coefficients alone. This is because reflectance is both a surface as well as a bulk phenomenon, incorporating both dispersion as well as absorption effects. The same spectral feature can even be observed as either a maximum or minimum. The complex effects depend on particle size and preparation, as well as the relative amplitudes of the optical constants n and k, i.e. the real and imaginary components of the complex refractive index. While somewhat oversimplified, upward-going amplitude in the reflectance spectrum usually results from surface scattering, i.e. rays that have been reflected from the surface without penetration, whereas downward-going peaks are due to either absorption or volume scattering, i.e. rays that have penetrated or refracted into the sample interior and are not reflected. While the effects are known, we report seminal measurements of reflectance along with quantified particle size of the samples, the sizing obtained from optical microscopy measurements. The size measurements are correlated with the reflectance spectra in the 1.3 -16 micron range for various bulk materials that have a combination of strong and weak absorption bands in order to understand the effects on the spectral features as a function of the mean grain size. We report results for both anhydrous sodium sulfate Na 2 SO 4 as well as ammonium sulfate (NH 4 ) 2 SO 4 ; the optical constants have been measured for (NH 4 ) 2 SO 4 . To go a step further from the laboratory and into the field we explore our understanding of particle size effects on reflectance spectra using standoff detection at distances of up to 160 meters in a field experiment. The studies have shown that particle size has a strong influence on the measured reflectance spectra of such materials; successful identification requires sufficient, representative reflectance data to include the particle sizes of interest.