Beyond guesswork: how accurate are surgeons at determining the degree of glenoid bone loss in instability surgery?

Background: Accurate measurement of glenoid bone loss (GBL) is critical to preoperative planning in cases of recurrent shoulder instability. The concept of critical bone loss has been established with a value of GBL >13.5% being associated with higher failure rate following arthroscopic Bankart Repair. Advanced imaging, such as magnetic resonance imaging (MRI) scans, can be used to quantify GBL prior to surgery using the best-fit circle technique. Surgeons have traditionally relied on visual inspection of the MRI scan preoperatively or on visual inspection of the glenoid at the time of arthroscopy to determine whether GBL is present. The purpose of this study is to determine if 3 fellowship-trained shoulder surgeons could adequately quantify GBL without using best-fit circle measurements on MRI. Methods: A retrospective review was performed which included 122 patients over an 8-year period that had an arthroscopic Bankart repair performed by 3 fellowship-trained surgeons. In all patients, preoperative MRI scans were retrospectively measured using best-fit circle technique to determine true GBL and compare that to the surgeons' preoperative and intraoperative estimation of GBL. Results: GBL was correctly identified in only 36% (18/50) of patients when the preoperative best-fit circle measurements were not made. Critical bone loss was missed in 9.8% (12/122) of patients in the study group. The estimated mean bone loss in that group by visual inspection was 11.3% compared to 16% true bone loss measured on MRI. Even in the 18 patients with some identified bone loss prior to surgery, critical bone loss was missed in 6 patients when using visual inspection of the MRI or intraoperative inspection alone. Conclusion: Simple visual inspection of glenoid images on MRI scan and visual inspection of the glenoid at the time of surgery are inaccurate in determining the true extent of GBL especially in cases of subtle bone deficiency. Preoperative planning is dependent on the exact degree of bone deficiency and measurement on the MRI scan using the best-fit circle technique is recommended in all cases of instability surgery.

Variability of glenoid labral tear patterns: a study of 280 sequential surgical cases.

BACKGROUND: Glenoid labrum tears are a common cause of shoulder pain and instability and tear patterns have historically been ascribed into categorical descriptions such as anterior, posterior, and superior labral tears (SLAP [superior labrum anterior and posterior]) with multiple subtypes. Although often quoted as representing no more than 10% of instabilities, posterior shoulder instability may be more common than previously recognized. The purpose of this study was to review observed labral tear patterns and compare incidence and morphologies to historical descriptions. METHODS: All patients undergoing arthroscopic or open labral repair (Current Procedural Terminology codes 29806, 29807, 23455, 23460, 23462, 23465) by 2 fellowship-trained shoulder surgeons from July 2012 to May 2019 were retrospectively reviewed. Labral tears were categorized into 3 groups: exclusively anterior to the midline of the glenoid, exclusively posterior, and those crossing the midline of the glenoid. Chief complaint, mechanism of injury, hand dominance, preoperative MRI interpretation by surgeon, and independent radiologist were analyzed for each tear type. RESULTS: During the 7-year period, 280 patients underwent arthroscopic or open labral repair. Sixty percent of tears were traumatic, with dislocation being the most common traumatic mechanism at 31.4%. Ten distinct tear patterns were identified: 3 types of 90° tears (anteroinferior, posteroinferior, and posterosuperior), 4 types of 180° tears (anterior, posterior, inferior, and SLAP), 2 types of 270° tears (anteroinferior and anterosuperior), and 360° labral tears. A total of 134 tears (47.9%) were classified as posterior, and 72 tears (25.7%) were anterior. Seventy-four tears (26.4%) were combined anterior-posterior tears. Labral tears involving some portion of the posterior labrum constituted 74% of tears. A significant association between tear location and primary complaint (P < .001) was noted. Patients with anterior tears complained of only instability in 62.5% of cases, and only pain in 22%. Patients with posterior labral tears complained primarily of pain in 68% of cases, and instability in 21%. There was an accurate preoperative diagnosis given by both radiologists and surgeons on 30% (n = 63) of the tears. CONCLUSION: There is a wide variety of labral tear patterns identified at the time of surgery, and the incidence of posterior labral tears is higher than previously described. Isolated Bankart lesions are relatively rare and are often associated with more extensive labral lesions. Patients with posterior labral pathology more often complain of pain rather than instability, whereas patients with anterior labral tears more often complain of instability.

Posterior Labral Repairs of the Shoulder Among Baseball Players: Results and Outcomes With Minimum 2-Year Follow-up.

BACKGROUND: There is a paucity of information regarding the treatment of posterior labral tears of the shoulder for baseball players. Reports regarding treatment and postoperative outcomes are more limited than its anterior and superior counterparts. PURPOSE: To evaluate the clinical presentation, surgical findings, postoperative outcomes, and rate of return to sport after arthroscopic repair of posterior labral injuries of the shoulder among baseball players. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Retrospective review was performed of baseball players who underwent arthroscopic posterior labral repair between 2009 and 2015 by a single surgeon, with a minimum 2-year follow-up. The group was composed of 32 male patients involved in recreational (6.3%), high school (43.8%), college (31.3%), and professional (18.8%) baseball, with a mean age of 20.5 years. Patients were categorized by chief complaint, clinical findings, surgical findings, and concomitant procedures performed. Pre- and postoperative measures included pain scale, range of motion, American Shoulder and Elbow Surgeons shoulder score, return to play, and patient satisfaction. RESULTS: A variety of tear patterns were identified; 32% involved 90° of the posterior superior labrum; 35% involved the posterior 180°; and 32% involved 90° of the posterior inferior labrum. The dominant mechanism of injury was throwing (34.4%). The most common chief complaint was pain (n = 25, 78%), followed by pain and instability symptoms (n = 6, 18.8%), with only 3% citing isolated sensation of instability. Magnetic resonance imaging clearly identified tear patterns in 75% of cases. American Shoulder and Elbow Surgeons scores significantly improved ( P < .0001), increasing on average 30.9 points from the preoperative mean of 65.4 to a postoperative mean of 96.3. No significant range of motion deficits were noted. Tear size and number of anchors utilized did not influence outcomes. Ninety-four percent of athletes returned to play, 61% at previous levels, and 6% did not return. Pitchers had a lower return to previous level of play than position players (41% vs 86%, P = .0113). CONCLUSION: Arthroscopic treatment of posterior labral tears of baseball players was effective in improving pain and function, resulting in 94% patient satisfaction and 94% return to sport, with 61% returning to previous level of play. Patient presentation is variable, with a majority of patients citing pain rather than instability.

Elbow Injuries in the Adolescent Thrower.

PURPOSE OF REVIEW: With an increasing rate of adolescent elbow injuries, especially in throwing athletes, the purpose of this review is to investigate the current literature regarding the diagnosis, treatment, and non-operative and operative outcomes of medial epicondyle fractures, ulnar collateral ligament repair, osteochondritis dissecans of the elbow, and olecranon stress fractures. RECENT FINDINGS: Acceptable outcomes with both non-operative and operative treatments of medial epicondyle fractures have been reported, with surgical indications continuing to evolve. Unstable osteochondritis dissecans lesions, especially in patients with closed growth plates, require operative fixation, and emerging open and arthroscopic techniques including lesion debridement, marrow stimulation, autograft transfer, and allograft transplantation are described with good outcomes. Ulnar collateral repair has emerged as an exciting treatment option for an avulsion of either end of the ligament in young throwing athletes, with faster rehabilitation times than traditional ulnar collateral ligament reconstruction. Olecranon stress fractures are increasing in prevalence, and when a non-operative treatment course is unsuccessful, athletes have a high return-to-play rate after percutaneous cannulated screw placement. With proper indications, non-operative and operative treatment modalities are reported with a high return-to-play and acceptable clinical outcomes for common elbow injuries, including medial epicondyle fractures, ulnar collateral ligament repair, osteochondritis dissecans of the elbow, and olecranon stress fractures, in adolescent throwing athletes. Further research is needed to better define treatment algorithms, surgical indications, and outcomes.

Controlling tunnelling in methane loss from acetone ions by deuteration.

Energetic acetone cations decay by methane or methyl radical loss. Although the methane-loss barrier to form the ketene cation is higher and the activation entropy is lower, it has a significant branching ratio at low energies thanks to quantum tunnelling. H-atom tunnelling can be selectively quenched and the methane-loss channel suppressed quantitatively by deuteration.

Effect of interference screw depth on fixation strength in biceps tenodesis.

PURPOSE: The purpose of this study was to assess the biomechanical performance of the long head of the biceps tenodesis with an interference screw with respect to screw depth. METHODS: Twenty-one human cadaveric shoulders were randomized into 3 treatment groups (7 each): interference screw placed flush to the humeral cortex, 50% proud, or fully recessed. Bone density was determined, and subpectoral biceps tenodesis was performed with 8 × 12 mm Bio-Tenodesis screws (Arthrex, Naples, FL). Each construct was cyclically loaded from 5 to 70 N for 500 cycles at 1 Hz and then pulled to failure at 1 mm/s. Relative actuator displacement was calculated from cyclic testing. Maximum load, elongation, linear stiffness, and failure mode were recorded from pull-to-failure testing. Because of numerous failures during cyclic testing, the final load data from the fully recessed group were not statistically analyzed. The remaining groups were compared by use of a 2-tailed, Student unpaired t test and χ(2) analysis. RESULTS: There was no significant difference in displacement among groups during cyclic testing. Five specimens in the recessed group failed during cyclic testing, whereas 2 specimens and 0 specimens failed in the proud and flush groups, respectively. The maximum loads sustained were 281.6 ± 77.8 N, 184.5 ± 56.3 N, and 209.1 ± 57.0 N for the flush group, 50% proud group, and recessed group (in those specimens surviving cyclical loading), respectively. CONCLUSIONS: Placement of a Bio-Tenodesis screw flush to the humeral cortex is preferred for maximum fixation strength in subpectoral biceps tenodesis. A screw placed to 50% depth may be effective in the laboratory setting, but recessed placement is more variable and requires additional fixation. The fully recessed group resulted in 5 of 7 failures during cyclical loading, with no specimens failing in the flush group. CLINICAL RELEVANCE: This study shows the importance of determining the optimal depth of interference screw placement during biceps tenodesis to obtain optimal biomechanical performance and reduce the risk of fixation failure.

From iron pentacarbonyl to the iron ion by imaging photoelectron photoion coincidence.

The dissociation dynamics of internal energy selected iron pentacarbonyl cations, Fe(CO)5(+), have been investigated using the imaging photoelectron photoion coincidence (iPEPICO) spectrometer at the Swiss Light Source. The molecular ion loses all five carbonyl ligands in sequential dissociations in the 8.5-20 eV photon energy range. The Fe(CO)5(+) parent ion is metastable at the onset of the first dissociation reaction on the time scale of the experiment. The slightly asymmetric and broad daughter ion time-of-flight distributions indicate parent ion lifetimes in the microsecond range, and are used to obtain an experimental dissociation rate curve. Further carbonyl losses were found to be fast at threshold. The fractional parent and daughter ion abundances as a function of the photon energy, that is, breakdown diagram, as well as the dissociation rates for the first CO loss were modeled using the statistical Rice-Ramsperger-Kassel-Marcus (RRKM) and statistical adiabatic channel model (SSACM) theories. The excess energy redistribution in the products was also taken into account in a statistical framework. The 0 K dissociative photoionization thresholds for the five carbonyl-loss channels were found to be 9.015 ± 0.024 eV, 10.199 ± 0.027 eV, 10.949 ± 0.033 eV, 12.282 ± 0.39 eV, and 13.821 ± 0.045 eV for the processes leading to Fe(CO)4(+), Fe(CO)3(+), Fe(CO)2(+), Fe(CO)(+), and Fe(+), respectively. The iron cation thermochemistry is well-known, and these onsets connect the bare metal ion to the other fragment ions as well as to the gas phase neutral Fe(CO)5.

The basic science and clinical applications of osteochondral allografts.

Indications for the use of osteochondral allografts for orthopaedic surgical applications are increasing with improved surgical techniques and advancing experience. Modern tissue banks have developed harvesting, processing, and storage methods that ensure an adequate, safe supply of grafts. Continued research is necessary to find a technique that maximizes chondrocyte viability and metabolism both during storage and implantation. The majority of published data on the use of osteochondral allografts has focused on the management of osteochondral defects about the knee. Successful outcomes following these procedures have led to increased interest in their application to pathology affecting other joints including the shoulder and ankle. The current paper aims to review the basic science and clinical applications of osteochondral allografts.

Long-Term Evaluation of Autologous Chondrocyte Implantation: Minimum 7-Year Follow-Up.

PURPOSE: The purpose of this study was to report the clinical outcomes of autologous chondrocyte implantation (ACI) procedures performed by a single orthopedic surgeon at a minimum of 7 years follow-up. METHODS: A retrospective review of prospectively collected data was performed on 29 patients who underwent ACI of the knee between the years of 1998 and 2003. Prospective data were collected to assess changes in standardized outcome measures preoperatively and 2, 4, and 7 years postoperatively. All patients enrolled in the study were also recruited to undergo physical examination when possible. RESULTS: The final cohort consisted of 29 patients with a mean final follow-up time of 8.40 years (range = 7.14-10.88 years). Comparing preoperative scores to 7-year postoperative values, the mean International Knee Documentation Committee (IKDC) score improved from 39.80 to 59.24 (P < 0.001), mean Tegner-Lysholm score increased from 48.07 to 74.17 (P < 0.001), SF-12 physical score improved from 40.38 to 48.66 (P < 0.001), and SF-12 mental score improved from 44.14 to 48.98 (P < 0.05). Significant improvement occurred in Knee Injury and Osteoarthritis Outcome Score (KOOS) pain (56.03 to 80.36), symptoms (54.19 to 74.75), activities of daily living (72.01 to 85.90), sports (23.34 to 55.34), and quality of life (24.56 to 56.03) (P < 0.001). In addition, 7-year postoperative scores were at or near levels seen at 2 years (mean = 2.16; range = 0.94-4.03 years) and 4 years (mean = 4.43; range = 2.16-5.88 years) postoperatively, reflecting durable improvement. Subjectively, on a scale of 1 to 10 (10 being completely satisfied), the mean postoperative satisfaction rate was 8.14. Additionally, 88.9% of the patients would elect to have this surgery again if the same problem was to occur in the contralateral joint. CONCLUSIONS: The results of ACI in patients who present with symptomatic, full-thickness chondral defects remain durable at a minimum of 7-year follow-up with persistent, high levels of patient satisfaction. LEVEL OF EVIDENCE: Case series; Level of evidence, IV.

Evolution of rotator cuff repair techniques: are our patients really benefiting?

The repair integrity of rotator cuff tears, which are a common disorder, is influenced by many biologic, environmental, and surgical factors. Surgery for rotator cuff repairs has evolved significantly over the past decade. The technical goals of rotator cuff repair include achieving high initial fixation strength, minimizing gap formation, and maintaining mechanical stability until biologic healing occurs. A variety of surgical techniques have been established to capitalize on certain aspects of these tenets and have been shown to provide biomechanical and biologic benefits; however, overall clinical outcomes may be dependent on certain tear characteristics. It is important for orthopaedic surgeons to be familiar with the natural history of rotator cuff disease to understand the various repair strategies and techniques and the outcomes associated with these procedures.

Surgical management of articular cartilage defects of the knee.

Articular cartilage defects of the knee present diagnostic and treatment challenges for orthopaedic surgeons. As new data and technologies become available, treatment algorithms are continually being refined. It is important to examine treatment recommendations from the current literature and understand surgical techniques for articular cartilage repair.

Multimedia article. The arthroscopic management of partial-thickness rotator cuff tears: a systematic review of the literature.

PURPOSE: There is currently limited information available in the orthopaedic surgery literature regarding the appropriate management of symptomatic partial-thickness rotator cuff tears. METHODS: A systematic search was performed in PubMed, EMBASE, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and the Cochrane Central Register of Controlled Trials of all published literature pertaining to the arthroscopic management of partial-thickness rotator cuff tears. Inclusion criteria were all studies that reported clinical outcomes after arthroscopic treatment of both articular-sided and bursal-sided lesions using a validated outcome scoring system and a minimum of 12 months of follow-up. Data abstracted from the selected studies included tear type and location (articular v bursal sided), treatment approach, postoperative rehabilitation protocol, outcome scores, patient satisfaction, and postoperative imaging results. RESULTS: Sixteen studies met the inclusion criteria and were included for the final analysis. Seven of the studies treated partial-thickness rotator cuff tears with debridement with or without an associated subacromial decompression, 3 performed a takedown and repair, 5 used a transtendon repair technique, and 1 used a transosseous repair method. Among the 16 studies reviewed, excellent postoperative outcomes were reported in 28.7% to 93% of patients treated. In all 12 studies with available preoperative baseline data, treatment resulted in significant improvement in shoulder symptoms and function. For high-grade lesions, the data support arthroscopic takedown and repair, transtendon repairs, and transosseous repairs, with all 3 techniques providing a high percentage of excellent results. Debridement of partial-thickness tears of less than 50% of the tendon's thickness with or without a concomitant acromioplasty also results in good to excellent surgical outcomes; however, a 6.5% to 34.6% incidence of progression to full-thickness tears is present. CONCLUSIONS: This systematic review of 16 clinical studies showed that significant variation is present in the results obtained after the arthroscopic management of partial-thickness rotator cuff tears. What can be supported by the available data is that tears that involve less than 50% of the tendon can be treated with good results by debridement of the tendon with or without a formal acromioplasty, although subsequent tear progression may occur. When the tear is greater than 50%, surgical intervention focusing on repair has been successful. There is no evidence to suggest a differential in outcome for tear completion and repair versus transtendon repair of these lesions because both methods have been shown to result in favorable outcomes. LEVEL OF EVIDENCE: Level IV, systematic review of Level IV studies.

Clinical cartilage restoration: evolution and overview.

BACKGROUND: Clinical cartilage restoration is evolving, with established and emerging technologies. Randomized, prospective studies with adequate power comparing the myriad of surgical techniques used to treat chondral injuries are still lacking and it remains a challenge for the surgeon treating patients to make evidence-based decisions. QUESTIONS/PURPOSES: We reviewed the history of the major cartilage repair/restorative procedures, indications for currently available repair/restorative procedures, and postoperative management. METHODS: We performed searches using MEDLINE and cartilage-specific key words to identify all English-language literature. Articles were selected based on their contributions to our current understanding of the basic science and clinical treatment of articular cartilage lesions or historical importance. We then selected 77 articles, two of which are articles of historical importance. RESULTS: Current cartilage restorative techniques include débridement, microfracture, osteochondral fragment repair, osteochondral allograft, osteochondral autograft, and autologous chondrocyte transplantation. Pending techniques include two-staged cell-based therapies integrated into a variety of scaffolds, single-stage cell-based therapy, and augmentation of marrow stimulation, each with suggested indications including lesion size, location, and activity demands of the patient. The literature demonstrates variable improvements in pain and function contingent upon multiple variables including indications and application. CONCLUSIONS: For the patient with symptomatic chondral injury, numerous techniques are available to the surgeon to relieve pain and improve function. Until rigorous clinical trials (prospective, adequately powered, randomized control) are available, treatment decisions should be guided by expert extrapolation of the available literature based in historically sound principles.

Rotator cuff repair augmentation using a novel polycarbonate polyurethane patch: preliminary results at 12 months' follow-up.

BACKGROUND: Preventing anatomic failure after rotator cuff repair (RCR) remains a challenge. Augmentation with a surgical mesh may permanently reinforce the repair and decrease failure rates. The purpose of this study is to assess the postoperative outcomes of open RCR augmented with a novel reticulated polycarbonate polyurethane patch. MATERIALS AND METHODS: Ten patients with supraspinatus tendon tears underwent open RCR augmented with a polycarbonate polyurethane patch secured in a 6-point fixation construct placed over the repaired tendon. Patients were evaluated with preoperative and postoperative outcome measures, including the Simple Shoulder Test, visual analog pain scale, American Shoulder and Elbow Surgeons shoulder score, Cumulative Activities of Daily Living score, and University of California, Los Angeles shoulder scale, as well as range of motion. Postoperative magnetic resonance imaging was used to evaluate repair status. RESULTS: Patients showed significant improvements in visual analog pain scale, Simple Shoulder Test, and American Shoulder and Elbow Surgeons shoulder scores at both 6 and 12 months postoperatively (P < .05 and P < .01, respectively). The University of California, Los Angeles postoperative score was good to excellent in 7 patients at 6 months and in 8 patients at 12 months. Range of motion in forward flexion, abduction, internal rotation, and external rotation was significantly improved at both 6 and 12 months postoperatively (P < .05 and P < .01, respectively). Magnetic resonance imaging at 12 months showed healing in 90%; one patient had a definitive persistent tear. We found no adverse events associated with the patch, including the absence of fibrosis, mechanical symptoms, or visible subacromial adhesions. DISCUSSION: The polycarbonate polyurethane patch was designed to support tissue in growth and enhance healing as shown by preclinical animal studies. Clinically, the patch is well tolerated and shows promising efficacy, with a 10% retear rate at the 12-month time point.

A large atomic chlorine source inferred from mid-continental reactive nitrogen chemistry.

Halogen atoms and oxides are highly reactive and can profoundly affect atmospheric composition. Chlorine atoms can decrease the lifetimes of gaseous elemental mercury and hydrocarbons such as the greenhouse gas methane. Chlorine atoms also influence cycles that catalytically destroy or produce tropospheric ozone, a greenhouse gas potentially toxic to plant and animal life. Conversion of inorganic chloride into gaseous chlorine atom precursors within the troposphere is generally considered a coastal or marine air phenomenon. Here we report mid-continental observations of the chlorine atom precursor nitryl chloride at a distance of 1,400 km from the nearest coastline. We observe persistent and significant nitryl chloride production relative to the consumption of its nitrogen oxide precursors. Comparison of these findings to model predictions based on aerosol and precipitation composition data from long-term monitoring networks suggests nitryl chloride production in the contiguous USA alone is at a level similar to previous global estimates for coastal and marine regions. We also suggest that a significant fraction of tropospheric chlorine atoms may arise directly from anthropogenic pollutants.

Glenohumeral Microfracture.

The treatment of symptomatic cartilage lesions in the glenohumeral joint presents a significant challenge due to poor healing characteristics. Diagnosis of glenohumeral chondral defects is not always clear, and while current imaging modalities are good, many lesions require arthroscopy to fully appreciate. Arthroplasty remains an effective treatment in low-demand patients; however, younger, higher demand individuals may be treated with less invasive reparative measures. This paper discusses the diagnosis of glenohumeral chondral pathology and presents the technique, rehabilitation, and available outcomes following microfracture in the shoulder.

Augmentation Strategies following the Microfracture Technique for Repair of Focal Chondral Defects.

The operative management of focal chondral lesions continues to be problematic for the treating orthopedic surgeon secondary to the limited regenerative capacity of articular cartilage. Although many treatment options are currently available, none fulfills the criteria for an ideal repair solution, including a hyaline repair tissue that completely fills the defect and integrates well with the surrounding normal cartilage. The microfracture technique is an often-utilized, first-line treatment modality for chondral lesions within the knee, resulting in the formation of a fibrocartilaginous repair tissue with inferior biochemical and biomechanical properties compared to normal hyaline cartilage. Although symptomatic improvement has been shown in the short term, concerns about the durability and longevity of the fibrocartilaginous repair have been raised. In response, a number of strategies and techniques for augmentation of the first-generation microfracture procedure have been introduced in an effort to improve repair tissue characteristics and reduce long-term deterioration. Recent experimental approaches utilize modern tissue-engineering technologies including local supplementation of chondrogenic growth factors, hyaluronic acid, or cytokine modulation. Other second-generation microfracture-based techniques use different types of scaffold-guided in situ chondroinduction. The current article presents a comprehensive overview of both the experimental and early clinical results of these developing microfracture augmentation techniques.

Dissociation dynamics of sequential ionic reactions: heats of formation of tri-, di-, and monoethylphosphine.

The sequential ethene (C2H4) loss channels of energy-selected ethylphosphine ions have been studied using threshold photoelectron photoion coincidence (TPEPICO) spectroscopy in which ion time-of-flight (TOF) distributions are recorded as a function of the photon energy. The ion TOF distributions and breakdown diagrams have been modeled in terms of the statistical RRKM theory for unimolecular reactions, providing 0 K dissociation onsets, E0, for the ethene loss channels. Three RRKM curves were used to model the five measurements, since two of the reactions differ only by the internal energy of the parent ion. This series of dissociations provides a detailed check of the calculation of the product energy distribution for sequential reactions. From the determined E0's, the heats of formation of several ethylphosphine neutrals and ions have been determined: Delta(f)H degrees 298K[P(C(2)H(5))3] = -152.7 +/- 2.8 kJ/mol, Delta(f)H degrees 298K[P(C(2)H(5))3+] = 571.6 +/- 4.0 kJ/mol, Delta(f)H degrees 298K[HP(C(2)H(5))2] = -89.6 +/- 2.1 kJ/mol, Delta(f)H degrees 298K[HP(C(2)H(5))2+] = 669.9 +/- 2.5 kJ/mol, Delta(f)H degrees 298K[H(2)PC(2)H(5)] = -36.5 +/- 1.5 kJ/mol, Delta(f)H degrees 298K[H(2)PC(2)H(5)+] = 784.0 +/- 1.9 kJ/mol. These values have been supported by G2 and G3 calculations using isodesmic reactions. Coupled cluster calculations have been used to show that the C2H4 loss channel, which involves a hydrogen transfer step, proceeds without a reverse energy barrier.

Photoion photoelectron coincidence spectroscopy of primary amines RCH2NH2 (R = H, CH3, C2H5, C3H7, i-C3H7): alkylamine and alkyl radical heats of formation by isodesmic reaction networks.

Alkylamines (RCH(2)NH(2), R = H, CH(3), C(2)H(5), C(3)H(7), i-C(3)H(7)) have been investigated by dissociative photoionization by threshold photoelectron photoion coincidence spectroscopy (TPEPICO). The 0 K dissociation limits (9.754 +/- 0.008, 9.721 +/- 0.008, 9.702 +/- 0.012, and 9.668 +/- 0.012 eV for R = CH(3), C(2)H(5), C(3)H(7), i-C(3)H(7), respectively) have been determined by preparing energy-selected ions and collecting the fractional abundances of parent and daughter ions. All alkylamine cations produce the methylenimmonium ion, CH(2)NH(2)+, and the corresponding alkyl free radical. Two isodesmic reaction networks have also been constructed. The first one consists of the alkylamine parent molecules, and the other of the alkyl radical photofragments. Reaction heats within the isodesmic networks have been calculated at the CBS-APNO and W1U levels of theory. The two networks are connected by the TPEPICO dissociation energies. The heats of formation of the amines and the alkyl free radicals are then obtained by a modified least-squares fit to minimize the discrepancy between the TPEPICO and the ab initio values. The analysis of the fit reveals that the previous experimental heats of formation are largely accurate, but certain revisions are suggested. Thus, Delta(f)Ho(298K)[CH(3)NH(2)(g)] = -21.8 +/- 1.5 kJ mol-1, Delta(f)Ho(298K)[C(2)H(5)NH(2)(g)] = -50.1 +/- 1.5 kJ mol(-1), Delta(f)Ho(298K)[C(3)H(7)NH(2)(g)] = -70.8 +/- 1.5 kJ mol(-1), Delta(f)Ho(298K)[C(3)H(7)*] = 101.3 +/- 1 kJ mol(-1), and Delta(f)Ho(298K)[i-C(3)H(7)*] = 88.5 +/- 1 kJ mol(-1). The TPEPICO and the ab initio results for butylamine do not agree within 1 kJ mol-1; therefore, no new heat of formation is proposed for butylamine. It is nevertheless indicated that the previous experimental heats of formation of methylamine, propylamine, butylamine, and isobutylamine may have been systematically underestimated. On the other hand, the error in the ethyl radical heat of formation is found to be overestimated and can be decreased to +/- 1 kJ mol(-1); thus, Delta(f)Ho(298K)[C(2)H(5).] = 120.7 +/- 1 kJ mol(-1). On the basis of the data analysis, the heat of formation of the methylenimmonium ion is confirmed to be Delta(f)Ho(298K)[CH(2)NH(2)+] = 750.3 +/- 1 kJ mol(-1).