Isopropyl Iodide Research Articles

A Direct Comparison of Reactivity and Mechanism in the Gas Phase and in Solution

Direct comparisons of the reactivity and mechanistic pathways for anionic systems in the gas phase and in solution are presented. Rate constants and kinetic isotope effects for the reactions of methyl, ethyl, isopropyl, and tert-butyl iodide with cyanide ion in the gas phase, as well as for the reactions of methyl and ethyl iodide with cyanide ion in several solvents, are reported. In addition to measuring the perdeutero kinetic isotope effect (KIE) for each reaction, the secondary alpha- and beta-deuterium KIEs were determined for the ethyl iodide reaction. Comparisons of experimental results with computational transition states, KIEs, and branching fractions are explored to determine how solvent affects these reactions. The KIEs show that the transition state does not change significantly when the solvent is changed from dimethyl sulfoxide/methanol (a protic solvent) to dimethyl sulfoxide (a strongly polar aprotic solvent) to tetrahydrofuran (a slightly polar aprotic solvent) in the ethyl iodide-cyanide ion S(N)2 reaction in solution, as the "Solvation Rule for S(N)2 Reactions" predicts. However, the Solvation Rule fails the ultimate test of predicting gas phase results, where significantly smaller (more inverse) KIEs indicate the existence of a tighter transition state. This result is primarily attributed to the greater electrostatic forces between the partial negative charges on the iodide and cyanide ions and the partial positive charge on the alpha carbon in the gas phase transition state. Nevertheless, in evaluating the competition between S(N)2 and E2 processes, the mechanistic results for the solution and gas phase reactions are strikingly similar. The reaction of cyanide ion with ethyl iodide occurs exclusively by an S(N)2 mechanism in solution and primarily by an S(N)2 mechanism in the gas phase; only approximately 1% of the gas phase reaction is ascribed to an elimination process.

Flash Pyrolysis of Ethyl, n-Propyl, and Isopropyl Iodides as Monitored by Supersonic Expansion Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometry

The thermal decomposition of ethyl and propyl iodides, along with select isotopomers, up to 1300 K was performed by flash pyrolysis with a 20-100 mus time scale. The pyrolysis was followed by supersonic expansion to isolate the reactive intermediates and initial products, and detection was accomplished by vacuum ultraviolet single photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). The products monitored, such as CH(3), CH(3)I, C(2)H(5), C(2)H(4), HI, I, C(3)H(7), C(3)H(6), and I(2), provide for the simultaneous and direct observation of molecular elimination and bond fission pathways in ethyl and propyl iodides. In the pyrolysis of ethyl iodide, both C-I bond fission and HI molecular elimination pathways are competitive at the elevated temperatures, with C-I bond fission being preferred; at temperatures >or=1000 K, the ethyl radical products further dissociate to ethene + H atoms. In the pyrolysis of isopropyl iodide, both HI molecular elimination and C-I bond fission are observed and the molecular elimination channel is more important at all the elevated temperatures; the isopropyl radicals produced in the C-I fission channel undergo further decomposition to propene + H at temperatures >or=850 K. In contrast, bond fission is found to dominate the n-propyl iodide pyrolysis; at temperatures >or=950 K the n-propyl radicals produced decompose into methyl radical + ethene and propene + H atom. Isotopomer experiments characterize the extent of surface reactions and verify that the HI molecular eliminations in ethyl and propyl iodides proceed by a C1, C2 elimination mechanism (the 1,2 intramolecular elimination).

Stereoselective alkylations of chiral nitro imine and nitro hydrazone dianions. Synthesis of enantiomerically enriched 3-substituted 1-nitrocyclohexenes.

Dianions of chiral nitro imines (generated by a combination of LDA and s-BuLi) underwent diastereoselective alkylation with methyl, butyl, isopropyl, allyl, and methallyl iodides. In contrast to the behavior of simple metalloenamines, the most selective auxiliary contained no coordinating groups but did possess a large steric difference between the two substituents. The yield and selectivity of the alkylations were improved by the addition of HMPA or DMPU. The use of (S)-1-naphthylethylamine as the auxiliary afforded the R absolute configuration of the alkylation products. This stereochemical outcome could be rationalized by simple steric approach controlled alkylation in a conformationally fixed, internally coordinated dianion. A SAMP nitro hydrazone gave poorer yields and selectivities.

Density Functional Theory Studies of Negishi Alkyl–Alkyl Cross-Coupling Reactions Catalyzed by a Methylterpyridyl-Ni(I) Complex

Density functional theory calculations were done to examine the potential energy surfaces of Ni(I)-catalyzed Negishi alkyl-alkyl cross-coupling reactions by using propyl iodide and isopropyl iodide as model alkyl electrophiles and CH 3ZnI as a model alkyl nucleophile. A four-step catalytic cycle involving iodine transfer, radical addition, reductive elimination, and transmetalation steps were characterized structurally and energetically. The reaction mechanism for this catalytic cycle appears feasible based on the calculated free energy profiles for the reactions. The iodine transfer step is the rate-determining step for the Ni(tpy)-CH 3 (tpy = 2,2'6',2''-terpyridine) reactions with alkyl iodides. For secondary alkyl electrophiles, the oxidative addition intermediate, Ni(III), prefers to undergo decomposition over reductive elimination, whereas for the primary alkyl electrophiles, Ni(III) prefers to undergo reductive elimination over decomposition based on comparison of the relative reaction rates for these two types of steps. In addition, thermodynamic data were employed to help explain why the yield of the coupled product is very low from the Ni(II)-alkyl halide reactions with organozinc reagents.

An improved preparation of 1-methyl-3-propylimidazolium iodide and its application in dye-sensitized solar cells

In this paper, we reported an improved preparation of 1-methyl-3-propylimidazolium iodide (MPII), which was the alkylation reaction of n-propyl iodide and 1-methylimidazole under solvent-free conditions by Teflon-lined, stainless autoclaves. It was shown that the resulting MPII was high pure, the conversion rate of 1-methylimidazole was close to 100% and the procedure was simple and eco-friendly. Moreover, the apparent diffusion coefficients of triiodide and iodide in the mixture with different ratios of MPII and 3-methoxypropionitrile were demonstrated by cyclic voltammetry using a Pt ultramicroelectrode. The dye-sensitized solar cells with the electrolyte, which was composed of 0.13 M I 2, 0.10 M LiI, 0.50 M 4- tert-butylpyrdine in the mixture of 3-methoxypropionitrile and MPII (weight ratio 0.65:1), gave short circuit photocurrent density of 14.82 mA/cm 2, open-circuit voltage of 0.69 V, and fill factor of 0.66, corresponding to the photoelectric conversion efficiency of 6.73% at the illumination (AM 1.5, 100 mW/cm 2).

Photofragment Translational Spectroscopy ofn-C3H7I andi-C3H7I near 280 and 304 nm

The photodissociation dynamics of propyl iodides n-C3H7I and i-C3H7I near 280 and 304 nm has been investigated with our mini-TOF photofragment translational spectrometer. When a single laser is applied for both the photodissociation of parent molecules and the REMPI of I atom photofragments, the TOF spectra of photofragments I*(2P1/2) and I (2P3/2) are obtained at four different wavelengths for these two iodides. For n-C3H7I, some small vibrational peaks are partially resolved (with separation of approximately 522 cm-1, corresponding to the RCH2 deformation frequency of the fragment n-C3H7) at 281.73, 279.71, and 304.67 nm. These results show that the RCH2 deformation is mostly excited. For i-C3H7I, we obtain some partially resolved vibrational peaks (with separation of approximately 352 cm-1, corresponding to the HC(CH3)2 out-of-plane bending frequency of the fragment i-C3H7) at 281.73 nm only. For n-C3H7I, the partitioning values of the available energy Eint/Eavl are 0.48 at 281.73 nm and 0.49 at 304.02 nm for the I* channel, and 0.52 at both 279.71 and 304.67 nm for the I channel. These energy partitioning values are comparable with the previous results at different wavelengths in the literature. For i-C3H7I, the Eint/Eavl values are 0.61 at 281.73 nm, 0.65 at 304.02 nm for the I* channel, and 0.62 at 279.71 nm, 0.49 at 304.67 nm for the I channel. The potential-energy-surface crossing and the beta values have also been discussed.

Novel Nano‐Structured Silica‐Based Electrolytes Containing Quaternary Ammonium Iodide Moieties

AbstractA series of new hybrid organic‐inorganic molecules were prepared either by grafting of aminopropyltriethoxysilane (APTS) on silica nanoparticles followed by quaternarization of the nitrogen with ethyl, heptyl and isopropyl iodides or by grafting of N,N,N‐triethyl‐3‐(triethoxysilyl)propan‐1‐aminium iodide and N,N,N‐tridodecyl‐3‐(triethoxysilyl)propan‐1‐aminium iodide onto the silica nanoparticles. These new materials were used as iodide sources in the preparation of electrolyte solutions for dye‐sensitized solar cells (DSSCs). The performance of DSSCs was studied as a function of the nature of the solvent, the nature of the dye, the concentration of the modified silica in the electrolyte system and the silica content introduced during the hybrid synthesis. An efficiency of 8.5 % was obtained for solar cells containing the triethyl ammonium iodide salt at a concentration of 1 M in either acetonitrile (AN) or 3‐methoxypropionitrile (MPN) under an illumination of 10 mW cm–2, the equivalent of 0.1 Sun at AM 1.5G. At 1 Sun (100 mW cm–2, efficiencies of 6.6 % and 5.1 % were recorded for the AN and MPN‐based electrolytes, respectively.

Amphiphilic perfluoroalkylated sulfones and sulfonate betaines

Two types of perfluoro alkyl-containing amphiphilic sulfones 7– 9 and 13– 15, respectively, and sulfonate betaines 23– 32 were prepared using 2-[(perfluoroalkyl)methyl]oxiranes ( 1–3, R F = C 4F 9, C 6F 13, C 8F 17) or 3-(perfluoroalkyl)propyl iodides ( 16 and 17, R F = C 6F 13, C 8F 17) as the starting compounds. The overall yields of two-step syntheses were above 90%. The compounds 7– 9 were prepared by the reaction of oxiranes 1– 3 with 2-sulfanylethan-l-ol and subsequent oxidation of intermediate sulfides. Similarly, the amphiphiles 13– 15 were obtained by analogous reaction of oxiranes 1– 3 with thiomorpholine and subsequent oxidation of the sulfur atom in the morpholine ring. In the syntheses of betaines 23– 32, the starting compounds 1– 3 or 16 and 17 were first reacted with dimethylamine followed by the ring-opening reaction of the intermediate fluoroalkyl(dimethyl)amines with propane-1,3- or butane-1,4-sultones.

Measurements and Modeling of DO2Formation in the Reactions of C2D5and C3D7Radicals with O2

Time-resolved production of HO2 and DO2 from the reactions of nondeuterated and deuterated ethyl and propyl radicals with O2 are measured as a function of temperature and pressure in the "transition region" between 623 and 748 K using the technique of laser photolysis/long path frequency modulation spectroscopy. Experimental measurements, using both pulsed-photolytic Cl-atom-initiated oxidation of ethane and propane and direct photolysis of ethyl, n-propyl, and isopropyl iodides, are compared to kinetic models based on the results of time-dependent master equation calculations with ab initio characterization of stationary points. The formation of DO2 and HO2 from the subsequent reaction of the alkyl radicals with O2 is followed by infrared frequency modulation spectroscopy. The concentration of I atoms is simultaneously monitored by direct absorption of a second laser probe on the spin-orbit transition. The kinetic models accurately describe the time scale and amplitude of the DO2 and HO2 formation resulting from C2D5 + O2, n-C3D7 + O2, i-C3D7 + O2, and i-C3H7 + O2. Overall, a very good level of agreement is found between theory and experiments over a wide range of temperatures, pressures, and O2 concentrations. Good agreement is also found between previous literature studies and the theory presented in this work except in the case of the high-temperature rate coefficients for the reaction of i-C3H7 + O2 to form propene. A reinvestigation of the high-temperature kinetics of the i-C3H7 + O2 reaction appears warranted. The results from the present work suggest that the theory for formation of HO2 from the reactions of ethyl and both isomeric forms of propyl radicals with O2 are very well established at this time. It is hoped that these reactions can now form the groundwork for the study and interpretation of larger and more complex R + O2 systems.

Determination of Spin−Orbit Branching Fractions in the Photodissociation of Halogenated Hydrocarbons

Two methods based on vacuum ultraviolet (vuv) photoionization are presented for the determination of the spin-orbit branching fractions of the halogen atom produced in the photodissociation of halogenated hydrocarbons. Both methods make use of differences in the photoionization cross sections of the 2P(3/2) ground state and the 2P(1/2) excited-state of the neutral halogen atom. In the first approach, measurements of the total photoionization signal of the halogen atom are made at several vuv wavelengths, and the difference in the wavelength dependences for the 2P(3/2) and 2P(1/2) atoms allows the extraction of the branching fractions. In the second approach, the vuv wavelength is set close to the ionization threshold of the 2P(3/2) atom (well above that of the 2P(1/2) atom), and measurements are made at several electric field strengths, which shift the ionization threshold and thus vary the photoionization cross sections. In both methods, the relative cross sections of the ground- and excited-state atoms are determined by using the known branching fractions for the 266 nm photodissociation of methyl iodide. These methods are applied to the photodissociation of isopropyl iodide and allyl iodide, two systems for which standard ion-imaging techniques do not provide unique branching fractions.

Sterically demanding bi- and tridentate alkoxy- N-heterocyclic carbenes

In contrast to the one-pot, two step syntheses we recently reported for a large number of substituted bidentate alkoxy–carbene ligands derived from epoxides, the reaction of imidazole with 2-adamantyl epoxide readily affords the bis(ethoxyadamantyl) substituted imidazolium salt [1-C{(NR)CHCH(NRH)}] (RH = CH 2(2-adamantyl)OH), which has been isolated and structurally characterised as its iodide salt, [HC{(NRH)CH} 2]I. Treatment with group 1 bases results in the loss of one ethoxy arm, to afford the structurally characterised monosubstituted alcohol imidazole, [HC{(NR)CHCHN}], or the lithium carbene complex [LiC{(NR)CHCHN}], a carbene complex containing a singly- N-functionalised alkoxy carbene. Alternatively, the monosubstituted alcohol imidazole may ben requaternised at the nitrogen atom with iso-propyl iodide to form [HC{(NRH)CHCH(NPr i )}]I, from which a more standard lithium alkoxycarbene complex [LiC{(NR)CHCHNPr i }] may be generated.

Near-threshold photoionization of hot isopropyl radicals

A combination of ion imaging and vacuum ultraviolet, single-photon ionization is used to study the internal energy dependence of the photoionization cross section of isopropyl radicals produced by the 266 nm photodissociation of isopropyl iodide. The isopropyl radicals so produced have internal energies of approximately 0.3-2.0 eV. Images recorded for photoionization energies from just below the adiabatic ionization threshold at 7.37+/-0.02 and 8.04 eV are essentially identical both to each other and to that recorded at 9.67 eV. These results imply that the photoionization cross section is only weakly dependent on internal energy. Several factors contributing to this observation are discussed, as are the implications for the photoionization of other systems with significant internal excitation.

Facile Synthesis of 3‐Substituted and 1,3‐Disubstituted Quinolin‐2(1H)‐ones from 2‐Nitrobenzaldehydes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Interaction of titanium(III) zwitterionic complex Cp[η 5-C 5H 4B(C 6F 5) 3]Ti with organic halides: Synthesis and X-ray crystal structure determination of zwitterionic titanocene monohalides Cp[η 5-C 5H 4B(C 6F 5) 3]TiX (X = Cl, Br) and their catalytic activity in the ring-opening polymerization of ε-caprolactone

The reaction of the titanium(III) zwitterionic complex Cp[η 5-C 5H 4B(C 6F 5) 3]Ti ( 1) with CCl 4 at 20 °C under Ar results in the formation of hexachloroethane and the zwitterionic titanocene monochloride Cp[η 5-C 5H 4B(C 6F 5) 3]TiCl ( 3) containing a B(C 6F 5) 3 moiety in the η 5-cyclopentadienyl ring. Under similar conditions, the reaction of 1 with 1,2-dibromoethane affords ethylene and the corresponding zwitterionic monobromide Cp[η 5-C 5H 4B(C 6F 5) 3]TiBr ( 4). An X-ray diffraction study of 3 and 4 revealed the presence of a coordinative bond between the ortho-fluorine atom of one of the C 6F 5 substituents and the positively charged titanium centre. In the interaction of 1 with n-propyl iodide at 20 °C, titanocene diiodide, B(C 6F 5) 3 and propylene are produced. The mechanism of this interesting reaction is discussed. The synthesized zwitterions 3 and 4 are able to catalyze the ring-opening polymerization of ε-caprolactone in a toluene solution and in bulk. The highest activity in this process is exhibited by 3. The first X-ray diffraction study of Cp 2TiI 2 has been carried out.

Facile Synthesis of 3-Substituted and 1,3-Disubstituted Quinolin-2(1H)-ones from 2-Nitrobenzaldehydes

2-Nitrobenzaldehydes were reduced with iron powder to 2-aminobenzaldehydes, which were reacted immediately with acyl chlorides to provide 2-carboxamidobenzaldehydes (1) with overall yields of 71-90 %. Reaction of 1 with base provided 3-substituted quinolin-2(1H)-ones with 63-97 % yields. Treatment of 1 with methyl iodide and base gave l-methyl-3-substituted quinolin-2(1H)-ones with 82-95 % yields, whereas the treatment with isopropyl iodide gave 1-isopropyl-3-substituted quinolin-2(1H)-ones with 7-42 % yields.

Synthesis and complexation of tetrakis(diphenylphosphinomethyl)calix[4]arene adopting the 1,3-alternate conformation

Novel upper-rim modified tetraphosphinocalix[4]arenes (5a–b) adopting 1,3-alternate conformation have been synthesized. Reaction of 5,11,17,23-tetrachloromethyl-25,26,27,28-tetrahydroxycalix[4]arene (1) with Ph2POEt gave 5,11,17,23-tetrakis(diphenylphosphinoylmethyl)-25,26,27,28-tetrahydroxycalix[4]arene (2). Tetra-O-substitution of 2 with n-propyl iodide or benzyl bromide in the presence of K2CO3 carried out to afford 5,11,17,23-tetrakis(diphenylphosphinoylmethyl)-25,26,27,28-tetrapropoxy-(3a) or -benzyloxycalix[4]arene (3b), whereas di-O-substituted calix[4]arene, 5,11,17,23-tetrakis(diphenylphosphinoylmethyl)-25,27-dipropoxy-26,28-dihydroxycalix[4]arene (4), was obtained exclusively when Na2CO3 was used as base. Reduction of 3a–b with PhSiHCl2 afforded 5,11,17,23-tetrakis(diphosphinomethyl)-25,26,27,28-tetrapropoxy-(5a) and -tetrabenzyloxycalix[4]arene (5b). 1H and 13C NMR analysis reveals that the phosphines (5a–b) and the tetra-O-substituted phosphine oxides (3a–b) adopt 1,3-alternate conformation, while the parent tetrahydroxy-(2) and the di-O-propylated phosphine oxide (4) adopt cone-conformation. The X-ray structure indicates that the calix[4]arene moieties in 4 a pinched-cone conformation in solid state. Complexation of the phosphine ligand (5a) with [RuCl2(p-cymene)]2 affords the tetranuclear complexes, [{RuCl2(p-cymene)}2·5a] (6), as 1,3-alternate conformer.

The photophysical characteristics of 2- butylamino-2-demethoxy-hypocrellin B

2- Butylamino-2-demethoxy-hypocrellin B (BAHB), is an efficient photodynamic sensitizer, excited singlet-state energies are determined from the overlap of the normalized from absorption and emission spectra to be 176.4 kJ mol −1 ( E S CT ) and 202.8 kJ mol −1 ( E S 1 ), respectively. The quantum yields of BAHB fluorescence are 0.0098 ( Φ f1) and 0.0076 ( Φ f2), respectively. The energies and quantum yields of excited triplet states of BAHB are examined from the external effect of heavy atom on its florescence emission in the mixture of n-propyl iodide and benzene. The energies of excited triplet states of BAHB are 134.4±10.5 kJ mol −1 ( E T CT ) and 158.6±10.5 kJ mol −1 ( E T 1 ), respectively. The quantum yields of excited triplet states of BAHB are 0.73±0.04 ( Φ T CT ) and 0.56±0.04 ( Φ T 1 ), respectively. Meanwhile, the kinetic constants of fluorescence emission, intersystem crossing and internal conversion are also calculated from relative equations.

Thermal Chemistry of 2-Propanol and 2-Propyl Iodide on Clean and Oxygen-Pretreated Ni(100) Single-Crystal Surfaces

The thermal chemistry of 2-propanol and 2-propyl iodide on clean and oxygen-pretreated Ni(100) single-crystal surfaces was studied by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and reflection−absorption infrared spectroscopy (RAIRS). 2-Propyl iodide was used as a precursor for the preparation of 2-propyl surface species, in analogy to chemistry reported for other halo hydrocarbons. Those 2-propyl groups were shown to convert to acetone on both oxygen- and hydroxide-covered Ni(100) surfaces by following a two step mechanism, starting with a facile oxygen insertion into the metal−alkyl bond. The resulting 2-propoxide surface moiety, an intermediate that can also be prepared via dehydrogenation of the hydroxyl group in adsorbed 2-propanol, is stable up to about 300 K, at which point it undergoes β-hydride elimination to acetone. Coadsorbed surface hydroxide facilitates the first oxygen insertion reaction, and surface oxygen enhances the latter conversion of 2-propoxide to acetone. Some alcohol dehydration to propene is also observed, presumably by reaction of two hydrogen-bonded alcohol molecules. These results point to the feasibility of designing nickel-based catalysts for the selective partial oxidation of hydrocarbons.

Asymmetric Synthesis with 6‐tert‐Butyl‐5‐methoxy‐6‐methyl‐3,6‐dihydro‐2H‐1,4‐oxazin‐2‐one as a New Chiral Glycine Equivalent: Preparation of Enantiomerically Pure α‐Tertiary and α‐Quaternary α‐Amino Acids

AbstractThe chiral oxazinone 2 has been developed as a new chiral glycine equivalent for the asymmetric synthesis of mono‐ and disubstituted α‐amino acids. It is derived from the α‐hydroxycarboxylic acid 1, which serves as a chiral auxiliary, and is easily accessible in enantiomerically pure form by optical resolution of the racemic compound (RS)‐1. For alkylation reactions, 2 was deprotonated with sBuLi or phosphazenic base. Subsequent treatment with alkyl halides yielded the monosubstituted compounds 13/14a−c, e, f, (ent)‐13d, (ent)‐14d, while a second alkylation step, via the corresponding enolates, provided the disubstituted compounds 17/18a−d. Both alkylation steps proceeded with good yields and excellent diastereoselectivities (up to 99% de) and even less reactive electrophiles such as isopropyl iodide could be used. The results obtained in this reaction supported the assumption that the enolate of 2, as well as those of the monosubstituted derivatives of 2, have less tendency to form the aggregates that hamper alkylation reactions with other systems with higher oxygen content. From the major diastereomers of both the mono‐ and the disubstituted derivatives of 2 the corresponding α‐amino acids 33a−c and 34a−d were obtained in high enantiomeric purity by hydrolytic cleavage of the oxazinone ring, accomplished either in two steps with aqueous TFA and aqueous NaOH or in one with either aqueous NaOH or 3 N HBr. Alkylation of the enolate ions of (S)‐2 or (R)‐2 with epichlorohydrins as bifunctional electrophiles provided the hydroxymethylenecyclopropyl derivatives 21 and 22. Hydrolysis of 21 and 22 afforded the free amino acids 35 and (ent)‐35. Reductive amination with aniline after oxidation of 21 and 22 to the corresponding aldehydes 24 and 26 provided the compounds 25 and 27, whereas Mitsunobu treatment of 21 and 22 with 1‐phenyl‐3‐(trifluoroacetyl)urea (28) afforded the urea derivatives 29 and 31. Hydrolysis of these compounds yielded the corresponding 1‐aminocylopropanecarboxylic acid derivatives 36/(ent)‐36 and (ent)‐37. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Kinetic study of the reactions of OH with the simple alkyl iodides: CH 3I, C 2H 5I, 1-C 3H 7I and 2-C 3H 7I

The atmospheric fate of biogenic species such as the alkyl iodides is controlled mainly by photolysis, and by oxidation initiated by attack of Cl atoms and/or OH radicals. In order to assess the contribution made by OH attack on the simpler alkyl iodides, the absolute second-order rate coefficients for the reactions (1) OH+ CH 3 I→ products, (2) OH+ C 2 H 5 I→ products, (3) OH+ 1-C 3 H 7 I→ products, (4) OH+ 2-C 3 H 7 I→ products. were determined. These reactions were studied at P=1.5 and 5 Torr and at room temperature (298±2 K) using a fast-flow discharge system with resonance-fluorescence detection of OH radicals. The absolute second-order rate coefficients are k 1=(0.99±0.20)×10 −13 cm 3 molecule −1 s −1, k 2=(7.7±1.0)×10 −13 cm 3 molecule −1 s −1, k 3=(25.0±3.0)×10 −13 cm 3 molecule −1 s −1and k 4=(16.0±2.0)×10 −13 cm 3 molecule −1 s −1. The reactions were pressure independent over the range measured. The major atmospheric global degradation pathway is photolysis, with OH-initiated oxidation gaining importance for the propyl iodides. The effects of variable [Cl] on a local scale are discussed.