An Analysis of Solicitations From Predatory Journals in Ophthalmology.

PURPOSE: To evaluate trends associated with email communication from potentially predatory publishers to faculty in ophthalmology. DESIGN: Cross-sectional study METHODS: Ophthalmologists (n = 14) from various subspecialties and institutions were recruited to participate. Participants identified unsolicited emails that they had received originating from publishers in May 2021. Information collected included details on email contents and publisher organizations. Trends in communications from predatory publishers were evaluated. RESULTS: Over a 30-day study period, a total of 1813 emails were received from 383 unique publishers and 696 unique journals, with a mean (SD) of 4.73 (2.46) emails received per day per participant. Of the 1813 emails identified, 242 (13%) emails were invitations to conferences, whereas 1440 (80%) were solicitations for article submissions to open-access, pay-to-publish journals. A total of 522 (29.0%) emails were related to ophthalmology, and reference to a prior publication of the participant occurred in 262 emails (14%). Of the 696 unique journals identified, 174 (25%) journals were indexed on PubMed and 426 (61%) were listed on Beall's list. When comparing journals that were listed on PubMed vs those that were not, PubMed indexed journals had a higher impact factor (2.1 vs 1.5, P = .002), were less likely to use "greetings" (76% vs 91%, P < .001), had fewer spelling/grammar errors (40% vs 51%, P = .01), and were less likely to offer rapid publication (16% vs 25%, P = .02). CONCLUSIONS: Unsolicited requests to publish occur frequently and may diminish the quality of the scientific literature. We encourage individuals in ophthalmology to be aware of these trends in predatory publishing.

Deep Learning-Assisted Diffusion Tensor Imaging for Evaluation of the Physis and Metaphysis.

Diffusion tensor imaging of physis and metaphysis can be used as a biomarker to predict height change in the pediatric population. Current application of this technique requires manual segmentation of the physis which is time-consuming and introduces interobserver variability. UNET Transformers (UNETR) can be used for automatic segmentation to optimize workflow. Three hundred and eighty-five DTI scans from 191 subjects with mean age of 12.6 years ± 2.01 years were retrospectively used for training and validation. The mean Dice correlation coefficient was 0.81 for the UNETR model and 0.68 for the UNET. Manual extraction and segmentation took 15 min per volume, whereas both deep learning segmentation techniques took < 1 s per volume and were deterministic, always producing the same result for a given input. Intraclass correlation coefficient (ICC) for ROI-derived femur diffusion metrics was excellent for tract count (0.95), volume (0.95), and FA (0.97), and good for tract length (0.87). The results support the hypothesis that a hybrid UNETR model can be trained to replace the manual segmentation of physeal DTI images, therefore automating the process.

CHARACTERISTICS OF PARTICIPANTS IN DIABETIC RETINOPATHY CLINICAL RESEARCH CLINICAL TRIALS WHO WERE LOST TO FOLLOW-UP.

PURPOSE: Our study describes the racial/ethnic composition and the broad health status/severity of disease of the cohorts of Diabetic Retinopathy Clinical Research clinical trials and compares the rates of noncompletion of the trial with the first data report (lost to follow-up). METHODS: This study is a retrospective cohort study of participants in Diabetic Retinopathy Clinical Research Retina Network clinical trials who met our inclusion criteria. The primary outcome was the lost to follow-up rates and their associated risk factors. RESULTS: Eight clinical trials with 3,492 participants met our inclusion criteria. Participants who were lost to follow-up were more likely to be younger, Hispanic or Black, had Type 1 diabetes mellitus, had worse baseline best-corrected visual acuity, had higher hemoglobin A1c, had higher blood pressure, and had proliferative diabetic retinopathy (PDR) (Diabetic Retinopathy Severity Score >66). CONCLUSION: Participants who were lost to follow-up during Diabetic Retinopathy Clinical Research clinical trials tended to be younger, Hispanic or Black, and had worse diabetes and hypertension. This study highlights the importance of ensuring that a representative population is maintained through the end of the study period.

An Interactive Module to Enhance Clinical and Non-clinical Communication Skills With LGBTQIA2S+ Patients.

The Lesbian, Gay, Transgender, Queer, Intersex, Asexual, Two-Spirit, and all others (LGBTQIA2S+) community comprises a diverse array of people who challenge conventional norms regarding sexual orientation and/or gender identity. This group possesses a distinct set of social and cultural principles that necessitate personalized and all-encompassing medical attention. In light of the increase in the number of individuals openly sharing their LGBTQIA2S+ identity and a growing societal openness toward this community, most healthcare providers do not feel prepared with the requisite knowledge and skills to appropriately care for the needs of this community. We describe the development of an educational intervention, the LGBTQIA2S+ Healthcare Module, to address this significant gap in health professions education. It offers current and future clinicians just-in-time training on the language and cultural context to adequately provide patient-centered care to this community.

MRI findings of growth plate fractures of the knee: are there age- and fracture-dependent differences?

OBJECTIVE: To investigate MRI findings in children with physeal fractures of the knee with respect to age, location, and articular involvement. METHODS: Children with physeal fractures who underwent knee MRI between 2008 and 2021 were included. Two radiologists retrospectively reviewed all examinations to determine articular involvement, findings of physeal instability (perichondral disruption, periosteal entrapment), and internal derangement (cruciate ligament injury, meniscal tear, chondromalacia). Independent samples t, Mann-Whitney U, Pearson's chi-square, and Fisher's exact tests were used to compare findings. RESULTS: Fifty-six patients (37 boys, 19 girls; mean age: 12.2 ± 2.5 years; 32 distal femur, 24 proximal tibial fractures) included 24(43%) intraarticular fractures. Fractures were more common in the tibia than the femur (67% versus 25%, p = 0.004) and intraarticular fractures were more common in older than younger children (13.1 ± 2.0 versus 11.5 ± 2.7 years, p = 0.01), to associate with chondromalacia (46% versus 12%, p = 0.02) and undergo surgery (33% versus 10%, p = 0.04) when compared to extraarticular fractures. Perichondral disruption (n = 44, 79%) and periosteal entrapment (n = 13, 23%) did not significantly differ based on location or articular involvement (p > 0.05). At a median follow-up of 17.5 months (interquartile range: 1.25-34), 3 patients (2 intraarticular, 1 extraarticular fractures) developed osteoarthritis, osteochondral lesion, and leg-length discrepancy from growth arrest, which required additional surgery. CONCLUSION: Intraarticular physeal fractures were more common with older children, associate with chondromalacia, and underdo surgical intervention when compared to extraarticular fractures of the knee. While MRI findings of physeal instability were common, no significant differences were found between fractures based on anatomic location or fracture pattern.

A Comparison of Ocular Complications after 0.7 mg Dexamethasone Implant versus 2 mg of Intravitreal Triamcinolone in Vitrectomized Eyes.

OBJECTIVE: To compare the rates of complications in eyes that received a dexamethasone (DEX) implant (0.7 mg) or intravitreal triamcinolone (IVT) (2 mg) to treat postvitrectomy macular edema (ME). DESIGN: Retrospective, comparative, case series. SUBJECTS: A total of 148 eyes (147 patients); 75 eyes (75 patients) in the DEX group and 73 eyes (72 patients) in the IVT group. METHODS: The medical records of patients who received an intravitreal DEX 0.7 mg (Ozurdex) or triamcinolone (2 mg) (Triesence) for postvitrectomy ME between July 2014 and December 2021 with a minimum follow-up of 3 months were reviewed. Ocular hypotony and ocular hypertension were defined as intraocular pressure of < 6 mmHg and > 24 mmHg, respectively. MAIN OUTCOME MEASURES: The rates of complications. RESULTS: The follow-up duration was 2.5 ± 1.6 years, with no significant difference between the groups (P = 0.398). The rate of transient ocular hypotony per eye and per injection was significantly higher in the DEX group (10 eyes [13%], 30 of 443 injections [7%]) compared with the IVT group (2 eyes [3%], 2 of 262 injections [0.8%]) (P = 0.039 and < 0.001, respectively). Mean visual acuity significantly decreased at the time of ocular hypotony (P = 0.031), but returned to preinjection level after resolution of the hypotony after a median of 12 days. The incidence of ocular hypertension was higher in the DEX group (23 eyes [31%]) than the IVT group (16 eyes [22%]), but this was not statistically significant (P = 0.307). Ocular hypertension was controlled with observation or topical medication. There were no between-group differences in the incidence of vitreous hemorrhage (DEX, 3 eyes [4%]; IVT, 1 eye [1%]; P = 0.632) or rhegmatogenous retinal detachment (DEX, 3 eyes [4%]; IVT, 0 eyes [0%]; P = 0.253). Four eyes (5%) experienced migration of the DEX implant into the anterior chamber. No eye developed endophthalmitis. CONCLUSION: The incidence of ocular hypotony, which causes transient visual impairment, was significantly higher in vitrectomized eyes treated with DEX compared with eyes treated with IVT. Injections other than the inferotemporal quadrant or rotating injection sites may be recommended. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found after the references.

Diffusion Tensor Imaging of the Knee to Predict Childhood Growth.

Background Accurate and precise methods to predict growth remain lacking. Diffusion tensor imaging (DTI) depicts the columnar structure of the physis and metaphyseal spongiosa and provides measures of tract volume and length that may help predict growth. Purpose To validate physeal DTI metrics as predictors of height velocity (1-year height gain from time of MRI examination) and total height gain (height gain from time of MRI examination until growth stops) and compare the prediction accuracy with bone age-based models. Materials and Methods Femoral DTI studies (b values = 0 and 600 sec/mm2; directions = 20) of healthy children who underwent MRI of the knee between February 2012 and December 2016 were retrospectively analyzed. Children with height measured at MRI and either 1 year later (height velocity) or after growth cessation (total height gain, mean = 34 months from MRI) were included. Physeal DTI tract volume and length were correlated with height velocity and total height gain. Multilinear regression was used to assess the potential of DTI metrics in the prediction of both parameters. Bland-Altman plots were used to compare root mean square error (RMSE) and bias in height prediction using DTI versus bone age methods. Results Eighty-nine children (mean age, 13 years ± 3 [SD]; 47 boys) had height velocity measured, and 70 (mean age, 14 years ± 1; 36 girls) had total height gain measured. Tract volumes correlated with height velocity (r2 = 0.49) and total height gain (r2 = 0.46) (P < .001 for both) after controlling for age and sex. Tract volume was the strongest predictor for height velocity and total height gain. An optimal multilinear model including tract volume improved prediction of height velocity (R2 = 0.63, RMSE = 1.7 cm) and total height gain (R2 = 0.59, RMSE = 1.8 cm) compared with bone age-based methods (height velocity: R2 = 0.32, RMSE = 2.9 cm; total height gain: R2 = 0.42, RMSE = 5.0 cm). Conclusion Models using tract volume derived from diffusion tensor imaging may perform better than bone age-based models in children for the prediction of height velocity and total height gain. © RSNA, 2022.

Magnetic resonance imaging findings of synovial sarcoma in children: location-dependent differences.

BACKGROUND: While overall survival for children is greater than that for adults, synovial sarcoma remains an aggressive neoplasm with a potentially poor prognosis, and its magnetic resonance imaging (MRI) findings in children are not well described. OBJECTIVE: We aimed to characterize the spectrum of MRI findings of synovial sarcoma in children with respect to anatomical location and outcome. MATERIALS AND METHODS: Children with histologically confirmed synovial sarcoma and preoperative MRI performed within the past 11 years (2009-2020) were included. Two radiologists retrospectively reviewed each MRI to categorize location, signal characteristics and associated findings. Chi-square and Fisher exact tests were used to assess associations with locations and outcomes. RESULTS: This study included 23 children (13 girls, 10 boys; mean age: 12.7±4.2 years) with 7 axial, 8 proximal and 8 distal appendicular lesions. Kappa ranged from 0.53 to 1. MRI findings differed significantly between locations with axial lesions measuring larger (P=0.01) and more likely to contain fluid levels (P=0.02), triple sign (P=0.02), inhomogeneous signal (T1-weighted images, P=0.003; T2-weighted images, P=0.02, contrast-enhanced images, P=0.03) with all lesions containing partially solid composition (P=0.03). At a median follow-up of 14 months (interquartile range: 7-33 months), 39% relapsed. Predictors of relapse (P<0.05) included metastasis at presentation, larger lesions, axial lesions and MRI findings of fluid level, T1-weighted hyperintensity, inhomogeneous signal (T1- and T2-weighted images) and poorly circumscribed margins. CONCLUSION: A significant association was found between location and MRI findings in our cohort of children with synovial sarcoma. Axial lesions were more likely to be larger, appear heterogeneous and be associated with a worse outcome.

Radiographic characterization of acute scaphoid fractures in children under 11 years of age.

BACKGROUND: Delayed diagnosis of scaphoid fractures can lead to long-term morbidity. While radiography is the preferred screening examination, there is a relative paucity of literature that examines fracture visibility in younger children, who have smaller ossification centers, an abundance of unossified cartilage and fractures that preferentially involve the distal scaphoid. OBJECTIVE: To characterize acute scaphoid fractures in younger children on radiographs with observer agreement and with respect to fracture location. MATERIALS AND METHODS: This institutional review board (IRB)-approved and Health Insurance Portability and Accountability Act (HIPAA)-compliant cross-sectional study included children (≤10 years of age) with acute scaphoid fractures (≤7 days), who underwent radiographic examinations at a tertiary children's hospital between December 2008 and June 2019. Three readers (two pediatric radiologists and one orthopedic surgeon) reviewed each examination to determine fracture visibility on each radiographic view and fracture location. Kruskal-Wallis, Fisher exact and Cochran-Armitage tests were used to compare fracture visibility and location, and Kappa tests were used to calculate observer agreement. RESULTS: Twenty-eight children (15 boys, 13 girls; mean age: 9.5±0.6 years) with 10 (36%) distal corner, 11 (39%) distal body and 7 (25%) mid-body fractures, underwent 7 (25%) 4-view, 18 (64%) 3-view and 3 (11%) 2-view examinations. Twenty-six (93%) fractures were visible on at least one view with six (21%) fractures visible on all available views. No significant association was found between fracture visibility and fracture location (P=0.32). Observer agreement was substantial to almost perfect. CONCLUSION: Only 7% of these acute scaphoid fractures in younger children are inconspicuous on the initial radiographic examination.

Pediatric scaphoid fracture: diagnostic performance of various radiographic views.

PURPOSE: The purpose of this study was to systematically investigate the performance of different radiographic views in the identification of scaphoid fractures in children. METHODS AND MATERIALS: This case-control study compared 4-view radiographic examinations of the wrist between children with scaphoid fracture and age- and sex-matched children without fractures performed between January 2008 and July 2019. After randomization, each examination was reviewed 3 times, at least 1 week apart, first using each view separately and later using multiple views without (3-view) and with the posteroanterior (PA) scaphoid view (4-view), to determine the presence or absence of a scaphoid fracture. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated with inter-rater agreement. RESULTS: The study group of 58 children (48 boys and 10 girls; mean age 13.1 ± 2.1 years) included 29 with scaphoid fractures (8 corner, 9 distal pole, 10 waist, and 2 proximal pole) and 29 without fractures. Multiple views had higher sensitivity (3-view, 93.0%; 4-view, 96.5%) for fracture identification when compared to individual views (41.0-89.6%). The oblique view was 100% specific for the identification of a scaphoid fracture, but it lacked sensitivity. The PA scaphoid view had the highest sensitivity (89.6%) and NPV (90%) when compared to other individual views and its inclusion in the 4-view examinations produced the highest inter-rater agreement (93%, κ = 0.86). CONCLUSION: Multiple radiographic views of the wrist with the inclusion of a PA scaphoid view (4-view) produced the highest sensitivity, NPV, and inter-rater agreement for the identification of a scaphoid fracture in children.

Hand Bone Age Radiography: Comparison Between Slot-scanning and Conventional Techniques.

BACKGROUND: Determination and longitudinal monitoring of progressive skeletal maturity are essential in the management of children with scoliosis. Although different methods for determining skeletal maturity exists, the most widely practiced method relies on the ossification pattern of the bones of the hand and wrist, which is traditionally acquired using conventional techniques and after the acquisition of the spine using the low-dose slot-scanning technique. Whereas the existing published literature has published promising results on the use of the slot-scanning technique to acquire these hand and wrist radiographs, image quality and radiation dose have not been systematically compared between these techniques. Thus, the objective of our study is to compare image quality, interpretation reliability, and radiation dose of hand bone age radiographs between slot-scanning and conventional techniques using age- and sex-matched children. METHODS: This retrospective study included children who underwent hand radiographs using slot-scanning between October 1, 2019 and December 31, 2019; and matched children who underwent conventional radiography. Blinded to technique, 5 readers reviewed all radiographs after randomization to rate image quality and to determine bone age using the Greulich and Pyle classification. Dose area product was recorded. Mann-Whitney and t tests were used to compare variables between techniques and intraclass correlation (ICC) to determine observer agreement. RESULTS: Our study cohort of 194 children (128 girls, 66 boys; mean age: 13.7±2.3 y) included 97 slot-scanning and 97 conventional radiographs. One (1%) slot-scanning and no conventional radiograph was rated poor in image quality. There was almost perfect interpretation reliability with slot-scanning with high interobserver (ICC=0.948) and intraobserver (ICC=0.996) agreements, comparable with conventional radiographs (ICCs=0.919 and 0.996, respectively). Dose area product (n=158) was lower (P<0.002) with slot-scanning than with conventional techniques. CONCLUSION: Almost perfect interobserver reliability and intraobserver reproducibility with slot-scanning radiographs (performed using significantly lower radiation doses) suggest that this technique for hand bone age determination can be a reliable adjunct to scoliosis monitoring. LEVEL OF EVIDENCE: Level III.

Magnetic resonance imaging features of intra-articular tenosynovial giant cell tumor in children.

BACKGROUND: Magnetic resonance imaging (MRI) plays a critical role in disease characterization of intra-articular tenosynovial giant cell tumor. OBJECTIVE: To characterize the MRI features of intra-articular tenosynovial giant cell tumor in children with respect to disease subtype and anatomical location. MATERIALS AND METHODS: This retrospective study included children with tenosynovial giant cell tumor who underwent preoperative MRI between January 2006 and May 2020. Two radiologists reviewed each examination to determine disease subtype, signal intensities and the presence of an effusion, osseous changes, chondromalacia, juxtacapsular disease and concomitant joint involvement. Fisher exact, Mann-Whitney U, and Kruskal-Wallis H tests were used to compare findings between subtypes and locations. RESULTS: Twenty-four children (16 girls, 8 boys; mean age: 13.1±3.8 years) with 19 knee and 5 ankle-hindfoot tenosynovial giant cell tumor had either diffuse (n=15) or localized (n=9) disease. An effusion (P=0.004) was significantly more common with diffuse than localized disease. There was no significant difference in MRI signal (P-range: 0.09-1) or other imaging findings (P-range: 0.12-0.67) between subtypes. Children with knee involvement were significantly more likely to present with diffuse disease while those with ankle-hindfoot involvement all presented with focal disease (P=0.004). Juxtacapsular (n=4) and concomitant proximal tibiofibular joint involvement (n=5) were observed with diffuse disease in the knee. Erosions (P=0.01) were significantly more common in the ankle than in the knee. CONCLUSION: In our study, diffuse tenosynovial giant cell tumor was more common than localized disease, particularly in the knee where juxtacapsular and concomitant proximal tibiofibular joint disease can occur.

Developmental dysplasia of the hip: can contrast-enhanced MRI predict the development of avascular necrosis following surgery?

OBJECTIVE: To investigate the performance of contrast-enhanced MRI for predicting avascular necrosis (AVN) of the treated femoral head after surgical reduction for developmental dysplasia of the hip (DDH) using qualitative and quantitative methods. METHODS AND MATERIALS: This IRB-approved, HIPAA compliant retrospective study included 47 children who underwent same-day contrast-enhanced MRI following unilateral surgical hip reduction between April 2009 and June 2018. Blinded to the clinical outcome, 3 reviewers (2 pediatric radiologists and 1 pediatric orthopedist) independently categorized the enhancement pattern of the treated femoral head. Signal intensities, measured using regions of interest (ROI), were compared between treated and untreated hips and percent enhancements were compared between hips that developed and did not develop AVN. Post-reduction radiographs were evaluated using Salter's criteria for AVN and Kalmachi and MacEwen's classification for growth disturbance. Non-parametric tests and Fisher exact test were used to compare enhancement values between AVN and non-AVN hips. Bonferroni correction was used for multiple comparisons. RESULTS: Ten (21%) out of the 47 children (7 boys and 40 girls; mean age 9.0 ± 4.7 months) developed AVN. Age at surgical reduction was significantly higher (p = 0.03) for hips that developed AVN. No significant differences were found in gender (p = 0.61), laterality (p = 0.46), surgical approach (p = 0.08), history of pre-operative bracing (p = 0.72), abduction angle (p = 0.18-0.44), enhancement pattern (p = 0.66-0.76), or percent enhancement (p = 0.41-0.88) between AVN and non-AVN groups. CONCLUSION: Neither enhancement pattern nor percent enhancement predicted AVN, suggesting that post-reduction conventional MRI does not accurately distinguish between reversible and permanent vascular injury.

Age-dependent changes in pediatric scaphoid fracture pattern on radiographs.

OBJECTIVE: To systematically investigate age-dependent changes in scaphoid fracture prevalence and fracture patterns on radiographs in children under 15 years of age. METHODS AND MATERIALS: This retrospective study included children with scaphoid fractures, who underwent radiographic examinations between May 1, 2009, and August 31, 2019. Blinded to outcome, all radiographs were reviewed to determine fracture visibility on initial radiographs; to characterize fracture location (distal corner, distal, mid, and proximal body) and orientation (horizontal oblique, transverse, and vertical oblique); and to identify the presence or absence of gap, displacement, and concomitant fractures. Demographic information and information on weight and height were collected. Mann-Whitney U, Kruskal-Wallis rank sum, chi-square, and post hoc tests were used to investigate associations between age, fracture characteristics, and BMI percentile. RESULTS: The study included 180 children (134 boys and 46 girls; 12.3 ± 1.4 years) with 59 (33%) distal corner, 42 (23%) distal, 76 (42%) mid, and 3 (2%) proximal body fractures. Younger children were more likely to present with distal corner and distal body fractures while older children with mid and proximal body fractures (p = 0.035). No association was found between age and fracture visibility (p = 0.246), fracture orientation (p = 0.752), presence of gap (p = 0.130), displacement (p = 0.403), or concomitant fractures (p = 0.588). Younger children with scaphoid fractures were more likely to be obese (n = 117; p = 0.038). CONCLUSION: Scaphoid fractures of the distal corner and distal body were significantly more common in younger children, who are more likely to be obese.

Osteochondral lesion of the talus in children: Are there MRI findings of instability?

PURPOSE: The purpose of our study was to investigate the performance of MRI findings to predict instability of osteochondral lesion of the talus (OLT) in children and the association between skeletal maturity and lesion stability. MATERIALS AND METHOD: This retrospective IRB-approved and HIPPA-compliant study included children with OLT, who underwent an ankle MRI examination between March 1, 2011, and May 31, 2018. Blinded to the clinical outcome, 2 radiologists retrospectively assessed each MRI study for the presence or absence of various features on the articular side, along the interface, and on the subchondral side of each lesion. Regional skeletal maturity was recorded. Lesion stability was classified using clinical and surgical findings. Mann-Whitney U, Chi-square, Fisher's exact, and Cochran-Armitage tests were used to compare demographic and MRI findings between children with stable and unstable lesions. RESULTS: Of the 48 ankles identified, 36 were stable (12.7 + 3.9 years) and 12 were unstable (14.2 + 1.6 years) lesions. None of the lesions presented as a detached fragment. Skeletal immaturity (p = 0.01) was significantly more common in stable than unstable lesions. No other MRI features were found to be significantly different between stable and unstable lesions, which included the presence of an effusion (p = 0.27), intra-articular body (p = 0.25), cartilage changes (p = 0.19), subchondral disruption (p = 0.51), T2-weighted signal intensity rim (p = 0.16), cysts (p = 0.48), marginal sclerosis (p = 0.70), and perilesional marrow edema (p = 0.17). CONCLUSION: Results from our study suggest that previously published OCD criteria using conventional MRI are not sufficient for predicting stability of OLT in children. Regional skeletal maturity and older age were more predictive of unstable lesions.

Structure, vibrational spectra, and unimolecular dissociation of gaseous 1-fluoro-1-phenethyl cations.

The multiple CF bond character of PhCFMe (+) ions has been examined by means of theory, vibrational spectroscopy of the gaseous ions, and unimolecular decomposition chemistry. Atoms in Molecules analysis of DFT wave functions gives a CF bond order of n = 1.25 (as compared with n = 1.38 for Me 2CF (+), relative to n = 1 for fluoromethane and n = 2 for diatomic CF (+)), which is consistent with calculations of adiabatic CF stretching frequencies (nu CF). Experimental gas phase IR spectra, recorded by means of resonant multiphoton dissociation (IRMPD) using a free-electron laser connected to an FTICR mass spectrometer, show good agreement with predicted band positions for five deuterated isotopomers of PhCFMe (+). Metastable ion decompositions of deuterated analogues of PhCFMe (+) show the same HF/DF loss patterns as those produced by IRMPD. The evidence supports the conclusion that PhCFMe ions retain structural integrity until they become sufficiently excited to dissociate, whereupon they undergo intramolecular hydrogen scrambling that is competitive with HF/DF expulsion. Relative rates of hydrogen transposition and unimolecular dissociation are extracted from relative experimental fragment ion abundances. The predominant decomposition pathway is inferred to operate via a five-center transition state, as opposed to a four-center transition state for HF loss from gaseous Me 2CF (+).

Stereochemical preferences in 4-center syn-eliminations from gaseous ions.

Concerted unimolecular eliminations from ionized sec-alkyl aryl ethers (ROAr (+*)) display a preference for producing double bonds with trans geometry. This preference can be assessed quantitatively, provided that a regioselective variant can be found. Expulsion of neutral alkenes via syn-elimination to give ionized ArOH does not exhibit a pronounced preference with regard to the direction of elimination. By contrast, ionized 2-hexyl p-trifluoromethylphenyl ether eliminates neutral ArOH regioselectively, giving ionized 2-hexenes rather than ionized 1-hexene. Vicinally monodeuterated 2-hexyl and 3-hexyl ethers were prepared as pure diastereomers. Metastable ion decompositions of their gaseous radical cations are compared over two different time windows. The regioselectivity for the 2-hexyl ether allows the geometric preference for the double bonds to be estimated based on the difference between the erythro and threo monodeuterated diastereomers ( trans/ cis = 2.0 for producing ionized 2-hexene from parent ions with the lowest internal energies). The 3-hexyl ethers and ionized 2- and 3-phenoxyoctanes also undergo stereoselective elimination but give experimental values that reflect their lack of regioselectivity. Examination of erythro/ threo combinations shows that GC/MS/MS has the ability to quantitate stereochemistry in mixtures containing both positional and stereoisomers.