Infrared signature of the hydroperoxyalkyl intermediate (·QOOH) in cyclohexane oxidation: An isomer-resolved spectroscopic study.

Infrared (IR) action spectroscopy is utilized to characterize carbon-centered hydroperoxy-cyclohexyl radicals (·QOOH) transiently formed in cyclohexane oxidation. The oxidation pathway leads to three nearly degenerate ·QOOH isomers, ß-, γ-, and δ-QOOH, which are generated in the laboratory by H-atom abstraction from the corresponding ring sites of the cyclohexyl hydroperoxide (CHHP) precursor. The IR spectral features of jet-cooled and stabilized ·QOOH radicals are observed from 3590 to 7010 cm-1 (∼10-20 kcal mol-1) at energies in the vicinity of the transition state (TS) barrier leading to OH radicals that are detected by ultraviolet laser-induced fluorescence. The experimental approach affords selective detection of ß-QOOH, arising from its significantly lower TS barrier to OH products compared to γ and δ isomers, which results in rapid unimolecular decay and near unity branching to OH products. The observed IR spectrum of ß-QOOH includes fundamental and overtone OH stretch transitions, overtone CH stretch transitions, and combination bands involving OH or CH stretch with lower frequency modes. The assignment of ß-QOOH spectral features is guided by anharmonic frequencies and intensities computed using second-order vibrational perturbation theory. The overtone OH stretch (2νOH) of ß-QOOH is shifted only a few wavenumbers from that observed for the CHHP precursor, yet they are readily distinguished by their prompt vs slow dissociation rates to OH products.

Infrared spectroscopy of the syn-methyl-substituted Criegee intermediate: A combined experimental and theoretical study.

An IR-vacuum ultraviolet (VUV) ion-dip spectroscopy method is utilized to examine the IR spectrum of acetaldehyde oxide (CH3CHOO) in the overtone CH stretch (2νCH) spectral region. IR activation creates a depletion of the ground state population that reduces the VUV photoionization signal on the parent mass channel. IR activation of the more stable and populated syn-CH3CHOO conformer results in rapid unimolecular decay to OH + vinoxy products and makes the most significant contribution to the observed spectrum. The resultant IR-VUV ion-dip spectrum of CH3CHOO is similar to that obtained previously for syn-CH3CHOO using IR action spectroscopy with UV laser-induced fluorescence detection of OH products. The prominent IR features at 5984 and 6081 cm-1 are also observed using UV + VUV photoionization of OH products. Complementary theoretical calculations utilizing a general implementation of second-order vibrational perturbation theory provide new insights on the vibrational transitions that give rise to the experimental spectrum in the overtone CH stretch region. The introduction of physically motivated small shifts of the harmonic frequencies yields remarkably improved agreement between experiment and theory in the overtone CH stretch region. The prominent features are assigned as highly mixed states with contributions from two quanta of CH stretch and/or a combination of CH stretch with an overtone in mode 4. The generality of this approach is demonstrated by applying it to three different levels of electronic structure theory/basis sets, all of which provide spectra that are virtually indistinguishable despite showing large deviations prior to introducing the shifts to the harmonic frequencies.

Vibrational spectroscopy and dissociation dynamics of cyclohexyl hydroperoxide.

Organic hydroperoxides (ROOH) are ubiquitous in the atmospheric oxidation of volatile organic compounds (VOCs) as well as in low-temperature oxidation of hydrocarbon fuels. The present work focuses on a prototypical cyclic hydroperoxide, cyclohexyl hydroperoxide (CHHP). The overtone OH stretch (2νOH) spectrum of jet-cooled CHHP is recorded by IR multiphoton excitation with UV laser-induced fluorescence detection of the resulting OH products. A distinctive IR feature is observed at 7012.5 cm-1. Two conformers of CHHP are predicted to have similar stabilities (within 0.2 kcal mol-1) and overtone OH stretch transitions (2νOH), yet are separated by a significant interconversion barrier. The IR power dependence indicates that absorption of three or more IR photons is required for dissociation of CHHP to cyclohexoxy (RO) and OH radical products. Accompanying high-level single- and multi-reference electronic structure calculations quantitatively support the experimental results. Calculations are extended to a range of organic hydroperoxides to examine trends in bond dissociation energies associated with RO + OH formation and compared with prior theoretical results.

Isomer-resolved unimolecular dynamics of the hydroperoxyalkyl intermediate (•QOOH) in cyclohexane oxidation.

The oxidation of cycloalkanes is important in the combustion of transportation fuels and in atmospheric secondary organic aerosol formation. A transient carbon-centered radical intermediate (•QOOH) in the oxidation of cyclohexane is identified through its infrared fingerprint and time- and energy-resolved unimolecular dissociation dynamics to hydroxyl (OH) radical and bicyclic ether products. Although the cyclohexyl ring structure leads to three nearly degenerate •QOOH isomers (ß-, γ-, and δ-QOOH), their transition state (TS) barriers to OH products are predicted to differ considerably. Selective characterization of the ß-QOOH isomer is achieved at excitation energies associated with the lowest TS barrier, resulting in rapid unimolecular decay to OH products that are detected. A benchmarking approach is employed for the calculation of high-accuracy stationary point energies, in particular TS barriers, for cyclohexane oxidation (C6H11O2), building on higher-level reference calculations for the smaller ethane oxidation (C2H5O2) system. The isomer-specific characterization of ß-QOOH is validated by comparison of experimental OH product appearance rates with computed statistical microcanonical rates, including significant heavy-atom tunneling, at energies in the vicinity of the TS barrier. Master-equation modeling is utilized to extend the results to thermal unimolecular decay rate constants at temperatures and pressures relevant to cyclohexane combustion.

Energetic and Spectroscopic Properties of Astrophysically Relevant MgC4H Radicals Using High-Level Ab Initio Calculations.

Considering the importance of magnesium-bearing hydrocarbon molecules (MgCnH; n = 2, 4, and 6) in the carbon-rich circumstellar envelopes (e.g., IRC+10216), a total of 28 constitutional isomers of MgC4H have been theoretically investigated using density functional theory (DFT) and coupled-cluster methods. The zero-point vibrational energy corrected relative energies at the ROCCSD(T)/cc-pCVTZ level of theory reveal that the linear isomer, 1-magnesapent-2,4-diyn-1-yl (1, 2Σ+), is the global minimum geometry on the MgC4H potential energy surface. The latter has been detected both in the laboratory and in the evolved carbon star, IRC+10216. The calculated spectroscopic data for 1 match well with the experimental observations (error ∼ 0.78%) which validates our theoretical methodology. Plausible isomerization processes happening among different isomers are examined using DFT and coupled-cluster methods. CASPT2 calculations have been performed for a few isomers exhibiting multireference characteristics. The second most stable isomer, 1-ethynyl-1λ3-magnesacycloprop-2-ene-2,3-diyl (2, 2A1, µ = 2.54 D), is 146 kJ mol-1 higher in energy than 1 and possibly the next promising candidate to be detected in the laboratory or in the interstellar medium in future.

A five-carbon unsaturated Criegee intermediate: synthesis, spectroscopic identification, and theoretical study of 3-penten-2-one oxide.

Biogenic alkenes, such as isoprene and α-pinene, are the predominant source of volatile organic compounds (VOCs) emitted into the atmosphere. Atmospheric processing of alkenes via reaction with ozone leads to formation of zwitterionic reactive intermediates with a carbonyl oxide functional group, known as Criegee intermediates (CIs). CIs are known to exhibit a strong absorption (π* ← π) in the near ultraviolet and visible (UV-vis) region due to the carbonyl oxide moiety. This study focuses on the laboratory identification of a five-carbon CI with an unsaturated substituent, 3-penten-2-one oxide, which can be produced upon atmospheric ozonolysis of substituted isoprenes. 3-Penten-2-one oxide is generated in the laboratory by photolysis of a newly synthesized precursor, (Z)-2,4-diiodopent-2-ene, in the presence of oxygen. The electronic spectrum of 3-penten-2-one oxide was recorded by UV-vis induced depletion of the VUV photoionization signal on the parent m/z 100 mass channel using a time-of-flight mass spectrometer. The resultant electronic spectrum is broad and unstructured with peak absorption at ca. 375 nm. To complement the experimental findings, electronic structure calculations are performed at the CASPT2(12,10)/aug-cc-pVDZ level of theory. The experimental spectrum shows good agreement with the calculated electronic spectrum and vertical excitation energy obtained for the lowest energy conformer of 3-penten-2-one oxide. In addition, OH radical products resulting from unimolecular decay of energized 3-penten-2-oxide CIs are detected by UV laser-induced fluorescence. Finally, the experimental electronic spectrum is compared with that of a four-carbon, isoprene-derived CI, methyl vinyl ketone oxide, to understand the effects of an additional methyl group on the associated electronic properties.

Patch-wise 3D segmentation quality assessment combining reconstruction and regression networks.

Purpose: General deep-learning (DL)-based semantic segmentation methods with expert level accuracy may fail in 3D medical image segmentation due to complex tissue structures, lack of large datasets with ground truth, etc. For expeditious diagnosis, there is a compelling need to predict segmentation quality without ground truth. In some medical imaging applications, maintaining the quality of segmentation is crucial to the localized regions where disease is prevalent rather than just globally maintaining high-average segmentation quality. We propose a DL framework to identify regions of segmentation inaccuracies by combining a 3D generative adversarial network (GAN) and a convolutional regression network. Approach: Our approach is methodologically based on the learned ability to reconstruct the original images identifying the regions of location-specific segmentation failures, in which the reconstruction does not match the underlying original image. We use conditional GAN to reconstruct input images masked by the segmentation results. The regression network is trained to predict the patch-wise Dice similarity coefficient (DSC), conditioned on the segmentation results. The method relies directly on the extracted segmentation related features and does not need to use ground truth during the inference phase to identify erroneous regions in the computed segmentation. Results: We evaluated the proposed method on two public datasets: osteoarthritis initiative 4D (3D + time) knee MRI (knee-MR) and 3D non-small cell lung cancer CT (lung-CT). For the patch-wise DSC prediction, we observed the mean absolute errors of 0.01 and 0.04 with the independent standard for the knee-MR and lung-CT data, respectively. Conclusions: This method shows promising results in localizing the erroneous segmentation regions that may aid the downstream analysis of disease diagnosis and prognosis prediction.

Finding a way forward with the community: qualitative inquiry in the generalized HIV epidemic in Mizoram, India.

Introduction: Mizoram, the northeastern State of India bordering Myanmar, is presently witnessing a burgeoning generalized HIV epidemic along with the highest State-level HIV prevalence among female sex workers (FSWs, 24.7%) and people who inject drugs (PWID,19.8%) in the country. The present study was conducted against such background to understand the current situation of HIV prevention and care services in Mizoram, and capture community voices as well as concerns so that the way forward could be informed appropriately. Methods: The study period was October through December 2020 (in the midst of COVID-restrictions) in the districts of Aizawl, Mamit, Kolasib, Lunglei, and Champhai where HIV prevalence crossed 1% among ante-natal clinic (ANC) attending women. Contrastingly, the national average HIV prevalence among ANC attendees is 0.24%, which formed the basis for selecting the aforementioned five high burden districts for this current inquiry. In-depth-interviews were conducted with community members and youth leaders, vulnerable and general population groups as well as HIV-program officials. Interviews were recorded, transcribed, translated and later coded for analysis following thematic approach. Results: The emerging issues were grouped in three thematic layers; (1) HIV vulnerability, (2) challenges pertaining to prevention and care services, and (3) program elements and future roadmap. Discrimination at the community level, unfriendly behavior of some of the HIV-service staff, occasional interruption in supplies of anti-retroviral treatment and sterile syringes and needles were voiced as deterrents to accessing HIV prevention and care services by the participants. Community engagement, based on restorative approach rather than retribution and ensuring enhanced performance of the district AIDS program control units emerged as necessary programmatic elements. Conclusion: This inquiry highlighted macro-social and structural forces contributing to stigma and discrimination toward people at risk of HIV. It is urgent that HIV-services are re-aligned through de-centralized district level innovations and creation of safer spaces at the physical, societal and familial level. These, even during the time of stress such as a pandemic, would help health services to remain resilient. HIV outreach, sensitization of the community leaders and health-care professionals through strategic communication and ownership of the communities in these endeavors appeared paramount.

New Carbenes and Cyclic Allenes Energetically Comparable to Experimentally Known 1-Azulenylcarbene.

1-Azulenylcarbene (18; 0 kJ mol-1) is experimentally known as the key reactive intermediate for the rearrangement reactions of aryl carbenes in the laboratory. Here, using coupled-cluster methods up to the fc-CCSD(T)/cc-pVTZ//fc-CCSD(T)/cc-pVDZ level, thirteen new carbenes and one new cyclic allene are theoretically identified within the C11H8 elemental composition that either energetically lie below or very close to 18. While the cyclic allene, bicyclo[5.4.0]undeca-2,3,5,7,9,11-hexene (1; -166 kJ mol-1), is the experimentally known lowest energy isomer, three other cyclic allenes, bicyclo[5.4.0]undeca-1,2,4,6,8,10-hexene (2; -100 kJ mol-1), bicyclo[5.4.0]undeca-1,3,4,6,8,10-hexene (3; -97 kJ mol-1), and bicyclo[6.3.0]undeca-1,2,4,6,8,10-hexene (13; -42 kJ mol-1), demand new experimental studies. In total, thirty-one isomers are studied in this work (within -166 to +15 kJ mol-1 from 18) and all are found to be polar (µ ≠ 0). Among these, 1H-benzo[7]annulen-1-ylidene (17; -4 kJ mol-1; µ = 5.24 D), bicyclo[5.4.0]undeca-2,4,6,8,11-pentaene-10-ylidene (24; 13 kJ mol-1; µ = 7.59 D), 5-methylene-naphthalen-1-ylidene (26; 15 kJ mol-1; µ = 5.32 D), 6-methylene-naphthalen-2-ylidene (27; -43 kJ mol-1; µ = 6.60 D), and 8-methylene-naphthalen-2-ylidene (28; -39 kJ mol-1; µ = 5.55 D) are competitively polar compared to 18 (µ = 5.39 D). Therefore, these carbene molecules are potential targets for rotational spectroscopists and radioastronomers. Considering the importance of naphthyl and azulenylcarbenes in reactive intermediate chemistry, mechanisms of different rearrangement reactions and plausible formation pathways of some of these new carbenes are studied in this work using density functional theory.

Internal Electric Field-Induced Formation of Exotic Linear Acetonitrile Chains.

The application of external electric and magnetic fields is a powerful tool for aligning molecules in a controlled way, if the thermal fluctuations are small. Here we demonstrate that the same holds for internal electric fields in a molecular cluster. The electric field of a single molecular dipole, HCl, is used to manipulate the aggregation mechanism of subsequently added acetonitrile molecules. As a result, we could form exotic linear acetonitrile (CH3CN) chains at 0.37 K, as confirmed by infrared spectroscopy in superfluid helium nanodroplets. These linear chains are not observed in the absence of HCl and can be observed only when the internal electric field created by an HCl molecule is present. The accompanying simulations provide mechanistic insights into steric control, explain the selectivity of the process, and show that non-additive electronic polarization effects systematically enhance the dipole moment of these linear chains. Thus, adding more CH3CN monomers even supports further quasi-linear chain growth.

Challenges and measures to improve interviewers' bias in large-scale demographic surveys in India: Some suggestions based on analysis of NFHS-4 data.

With increasing demand for more data at local level, the health surveys have expanded both their coverage and areas of inquiry. To cater to this demand, the sample size in National Family Health Surveys (NFHS) increased significantly and thereby raised concerns regarding quality. The present paper attempts to investigate the presence of interviewers' bias in the birth history data in 4th round of NFHS in four states -Haryana, Odisha, Tamil Nadu and Maharashtra. The paper suggests a practical procedure that can be used to promote judicious supervision to minimize the non-sampling errors in future rounds of NFHS or other large-scale demographic surveys. Findings show that the outlier-based approach adopted in the paper helps in detecting the presence of interviewers' bias in the enumeration of total children ever born as well as those born during 5 years prior to the survey - two critical variables in demographic surveys. Among the four study states, the extent of the bias was highest in Tamil Nadu. In fact, in Haryana, the data was found to be free of any bias in the recording of the occurrence of births in 5 years preceding the survey. It is suggested that it should be feasible to employ the outlier-based approach early when fieldwork is in progress, along with usual practice of generating field check tables. This approach would have the potential to not only streamline the supervision but also help salvage the data from any biasing effects. The biasing effects, if any and found early during fieldwork can be rectified by suitably arranging the necessary revisits to the respondents.

Chiral Squaramide Catalyzed Asymmetric Spiroketalization toward Aromatic [6,5] Spiroketals.

Herein is disclosed an efficient enantio- and diastereoselective spiroketalization of aromatic ketone tethered to ortho-homoformyl and enone moiety via in situ enol formation using quinine derived squaramide organocatalyst to access aromatic [6,5] spiroketals with complete atom economy. Furthermore, aromatic spiroketals undergo Brønsted acid catalyzed Piancatelli type rearrangement to provide dihydronaphtho[1,2-b]furans with retention of the enantioselectivities.

Zwitter Ionization of Glycine at Outer Space Conditions due to Microhydration by Six Water Molecules.

We investigate glycine microsolvation with water molecules, mimicking astrophysical conditions, in our laboratory by embedding these clusters in helium nanodroplets at 0.37 K. We recorded mass selective infrared spectra in the frequency range 1500-1800 cm^{-1} where two bands centered at 1630 and 1724 cm^{-1} were observed. By comparison with the extensive accompanying calculations, the band at 1630 cm^{-1} was assigned to the COO^{-} asymmetric stretching mode of the zwitter ion and the band at 1724 cm^{-1} was assigned to redshifted C=O stretch within neutral clusters. We show that zwitter ion formation of amino acids readily occurs with only few water molecules available even under extreme conditions.

HIV epidemic in Mizoram, India: A rapid review to inform future responses.

Background & objectives: Mizoram, a northeastern State of India bordering Myanmar, is home to several tribal clans under the ethnic group Mizo: Renthelei, Ralte, Paite, Lai, Hmar, Lusei, Mara, Thado and Kuki. Mizos also reside in the neighbouring northeastern States of Tripura, Assam, Manipur and Nagaland. The majority of Mizo people outside India live across the border in the neighbouring Chin State and Sagaing Region of Myanmar. Over the last decade, Mizoram witnessed a concerning level of rise in HIV prevalence among the general population. The present rapid review was conducted to identify various interventions that could help curb this rising trend. Methods: An electronic search strategy with broad domains of 'HIV/AIDS', 'key population', 'community engagement' and 'interventions in Mizoram' using PubMed, Embase and Cochrane was adopted; grey literature were also accessed. Evidence, thus gleaned, were synthesized. Results: Twenty eight resource materials comprising articles, reports and dissertations contributed to the current review. Changing tribal social support structure, early initiation of drugs, sexual debut at an early age and drug-sex interface were identified as factors associated with the progression of HIV epidemic in the State. Issues pertaining to the migration of people across the borders and easy access to drugs continue to be of concern. Churches and youth leaders have a strong influence on the society, at times even constraining access of key population groups to HIV prevention and care services. Tackling stigma and discrimination, ensuring uninterrupted HIV services and creation of an enabling environment in this context seems urgently needed. Incarcerated people in the State have been found with a high level of HIV infection and their linkages with prevention and care services need strengthening. Interpretation & conclusions: This review underscores the importance of drawing upon successful intervention examples from the past such as 'Friends on Friday' and Red Ribbon Clubs. Active engagement of community-based organizations in programme planning, implementation and monitoring is essential. Establishment of harm reduction interventions for general and key populations paired with strategic communication appear to be the need of the hour.

An infrared spectroscopic study of trifluoromethoxybenzene⋯methanol complexes formed in superfluid helium nanodroplets.

We have studied the intermolecular complex formation between trifluoromethoxybenzene and methanol (CD3OD) in superfluid helium droplets by infrared spectroscopy in the spectral range of 2630-2730 cm-1, covering the O-D stretches of methanol-d4 (CD3OD). The cluster size associated with the observed bands is deduced from the variation of infrared intensity of a particular band with the partial pressures of trifluoromethoxybenzene and methanol. Quantum chemical calculations are performed at the MP2/6-311++G(d,p) level of theory to complement the experimental results. As a result, we have identified six different conformers of the trifluoromethoxybenzene⋯methanol intermolecular complex: three bound via O-H⋯O hydrogen bonds and the other three via O-H⋯π hydrogen bonds. Furthermore, to access the effect of fluorination on the methyl unit of anisole molecules, we compare the IR spectrum of trifluoromethoxybenzene (C6H5OCF3)⋯methanol with our earlier reported spectrum of anisole (C6H5OCH3)⋯methanol.

Vibrational Spectroscopy of Benzonitrile-(Water)1-2 Clusters in Helium Droplets.

Polycyclic aromatic hydrocarbons are considered as primary carriers of the unidentified interstellar bands. The recent discovery of the first interstellar aromatic molecule, benzonitrile (C6H5CN), suggests a repository of aromatic hydrocarbons in the outer earth environment. Herein, we report an infrared (IR) study of benzonitrile-(D2O)n clusters using mass-selective detection in helium nanodroplets. In this work, we use isotopically substituted water, D2O, instead of H2O because of our restricted IR frequency range (2565-3100 cm-1). A comparison of the experimental and predicted spectra computed at the MP2/6-311++G(d,p) level of benzonitrile-(water)1-2 clusters reveals the formation of a unique local minimum structure, which was not detected in previous gas-phase molecular beam experiments. Here, the solvent water forms a nearly linear hydrogen bond (H-bond) with the nitrile nitrogen of benzonitrile, while the previously reported most stable cyclic H-bonded isomer is not observed. This can be rationalized by the stepwise aggregation process of precooled monomers. The addition of a second water molecule results in the formation of two different isomers. In one of the observed isomers, a H-bonded water chain binds linearly to the nitrile nitrogen similar to the monohydrated benzonitrile-water complex. In the other observed isomer, the water dimer forms a ring-type structure, where a H-bonded water dimer simultaneously interacts with the nitrile nitrogen and the adjacent ortho CH group. Finally, we compare the water-binding motif in the neutral benzonitrile-water complex with the corresponding positively and negatively charged benzonitrile-water monohydrates to comprehend the charge-induced alteration of the solvent binding motif.

Unravelling the microhydration frameworks of prototype PAH by infrared spectroscopy: naphthalene-(water)1-3.

Hydration of aromatic molecules is a fundamental chemical process. Herein, microhydration framework of the prototypical neutral polycyclic aromatic hydrocarbon (PAH), naphthalene (naphthalene-(water)n≤3), is investigated by infrared spectroscopy inside helium nanodroplets. The measured data are analyzed by quantum chemical calculations at the MP2/6-311++G(d,p) level. This combined experimental and theoretical approach demonstrates that water binds to the naphthalene ring via π hydrogen bond (H-bond) for n = 1 case. Further addition of the solvent molecules occurs via the formation of a H-bonded water network facilitated by the nonadditive cooperative force. No isomers are observed in which the solvent molecules separately bind to the aromatic ring. For n = 3 case, we observe the formation of a cyclic H-bonded water moiety. Comparison with corresponding cationic and anionic naphthalene±-(water)n clusters demonstrates the charge-induced modification of the hydration motif. Our results are further compared with the prototypical benzene-(water)n complexes to comprehend the effect of an additional phenyl ring on the solvation network.

Stepwise Microhydration of Isoxazole: Infrared Spectroscopy of Isoxazole-(Water)n≤2 Clusters in Helium Nanodroplets.

Hydration of heterocyclic molecules plays a crucial role in biological and chemical recognition. Here, we present an infrared (IR) spectroscopic investigation of microhydrated, heterocyclic isoxazole molecule. The IR spectra of isoxazole-(water)n≤2 clusters are recorded using helium nanodroplet spectroscopy and are analyzed by quantum chemical calculations at the MP2/6-311++g(d,p) level. In the most abundant isoxazole-water dimer, the solvent water participates in a N···HO hydrogen bonding (H-bond) interaction, while in another observed structure, water simultaneously interacts with ring nitrogen and the neighboring CH group via N···HO and CH···O H-bonds. The addition of another water molecule to the monohydrated cluster results in the formation of a single isomer that features a seven-membered ring, in which the water dimer simultaneously interacts with skeletal nitrogen and the adjacent CH group through N···HO and CH···O bonds.

Six Low-Lying Isomers of C11H8 Are Unidentified in the Laboratory-A Theoretical Study.

Isomers of C11H8 have been theoretically examined using density functional theory and coupled-cluster methods. The current investigation reveals that 2aH-cyclopenta[cd]indene (2), 7-ethynyl-1H-indene (6), 4-ethynyl-1H-indene (7), 6-ethynyl-1H-indene (8), 5-ethynyl-1H-indene (9), and 7bH-cyclopenta[cd]indene (10) remain elusive till date in the laboratory. The puckered low-lying isomer 2 lies at 9 kJ mol-1 below the experimentally known molecule, cyclobuta[de]naphthalene (3), at the fc-CCSD(T)/cc-pVTZ//fc-CCSD(T)/cc-pVDZ level of theory. 2 lies at 36 kJ mol-1 above the thermodynamically most stable and experimentally known isomer, 1H-cyclopenta[cd]indene (1), at the same level. It is identified that 1,2-H transfer from 1 yields 2H-cyclopenta[cd]indene (14) and subsequent 1,2-H shift from 14 yields 2. Appropriate transition states have been identified, and intrinsic reaction coordinate calculations have been carried out at the B3LYP/6-311+G(d,p) level of theory. Recently, 1-ethynyl-1H-indene (11) has been detected using synchrotron-based vacuum ultraviolet ionization mass spectrometry. 2-Ethynyl-1H-indene (4) and 3-ethynyl-1H-indene (5) have been synthetically characterized in the past. While the derivatives of 7bH-cyclopenta[cd]indene (10) have been isolated elsewhere, the parent compound remains unidentified till date in the laboratory. Although C11H8 is a key elemental composition of astronomical interest for the formation of polycyclic aromatic hydrocarbons in the interstellar medium, none of its low-lying isomers have been characterized by rotational spectroscopy though they are having a permanent dipole moment (µ ≠ 0). Therefore, energetic and spectroscopic properties have been computed, and the present investigation necessitates new synthetic studies on C11H8, in particular 2, 6-10, and also rotational spectroscopic studies on all low-lying isomers.

A close competition between O-HO and O-Hπ hydrogen bonding: IR spectroscopy of anisole-methanol complex in helium nanodroplets.

Anisole is a multifunctional molecule that can form intermolecular complexes via its aromatic π-electron system as well as its methoxy group. We have studied the complexation of anisole with methanol. This serves as a prototype system to explore the competition between O-HO, O-Hπ, C-HO and C-Hπ hydrogen bonding. The anisolemethanol molecular complexes were formed in superfluid helium droplets and were detected using high-resolution laser-infrared spectroscopy, in the frequency range between 2630 and 2730 cm-1 covering the O-D stretches of methanol-d4 (CD3OD). Several bands assigned to (anisole)m(methanol)n complexes (where m = 1, and 2 and n = 1) were observed. The experimental results are complemented by the ab initio electronic structure calculations at the MP2/6-311++G(d,p) and B3LYP-D3/aug-cc-pVTZ levels of theory. Based on a comparison of the observed spectra with the ab initio theoretical spectra, we suggest that for the anisolemethanol complex, structures bound via O-HO and O-Hπ hydrogen bonding are almost equally preferred.