Radiographic and functional evaluation of low profile dorsal versus volar plating for distal radius fractures

INTRODUCTION

Fracture of the distal radius is a common clinical problem. Complex fracture requires open reduction and stabilization with plating to restore anatomy. Dorsal plating has advantages of buttressing the fracture better but often complicated with tendon problems as per literature. The rate of complications however, was not compared between the low-profile dorsal and the volar plates.

METHODOLOGY

This was a retrospective study on seventy one patients with dorsally angulated or displaced distal radius fractures, who underwent fixation of fractures with either dorsal or volar locking plate from Jan - Nov 2012. Preoperative radiographs were classified based on Universal and Fernandez classification. Postoperative radiographs were assessed for anatomical restoration of Radial length, radial inclination and volar tilt. Tendon and nerve related complications were assessed and functional evaluation was performed on the basis of PRWE (Patient related wrist evaluation) score.

RESULTS

Both groups were matched for their demographic profile and fracture types (p 0.033). Dorsal plating group had 89% excellent/good restoration and fair in 11%. Volar group had 96% excellent/good restoration and fair in 4%. Statistical analysis was performed with unpaired t test for radiographic parameters. Three patients had tendon related complications in dorsal plating group; two patients in volar group had nerve related complications. Functional outcome with PRWE was comparable between two groups.

CONCLUSION

Results with low profile dorsal plating were comparable to volar plating. Therefore dorsal plating can be used as an alternative method when dorsal buttressing of comminuted fracture is required, especially with concomitant osteoporosis.

Current scenario of spurious and substandard medicines in India: a systematic review

Globally, every country is the victim of substandard or spurious drugs, which result in life threatening issues, financial loss of consumer and manufacturer and loss in trust on health system. The aim of this enumerative review was to probe the extent on poor quality drugs with their consequences on public health and the preventive measures taken by the Indian pharmaceutical regulatory system. Government and non-government studies, literature and news were gathered from journals and authentic websites. All data from 2000 to 2013 were compiled and interpreted to reveal the real story of poor quality drugs in India. For minimizing spurious/falsely-labelled/falsified/counterfeit drugs or not of standard quality drugs, there is urgent requirement of more stringent regulation and legal action against the problem. However, India has taken some preventive steps in the country to fight against the poor quality drugs for protecting and promoting the public health.

Salivary proteins of plant-feeding hemipteroids - implication in phytophagy

Many hemipteroids are major pests and vectors of microbial pathogens, infecting crops. Saliva of the hemipteroids is critical in enabling them to be voracious feeders on plants, including the economically important ones. A plethora of hemipteroid salivary enzymes is known to inflict stress in plants, either by degrading the plant tissue or by affecting their normal metabolism. Hemipteroids utilize one of the following three strategies of feeding behaviour: salivary sheath feeding, osmotic-pump feeding and cell-rupture feeding. The last strategy also includes several different tactics such as lacerate-and-flush, lacerate-and-sip and macerate-and-flush. Understanding hemipteroid feeding mechanisms is critical, since feeding behaviour directs salivary composition. Saliva of the Heteroptera that are specialized as fruit and seed feeders, includes cell-degrading enzymes, auchenorrhynchan salivary composition also predominantly consists of cell-degrading enzymes such as amylase and protease, whereas that of the Sternorhyncha includes a variety of allelochemical-detoxifying enzymes. Little is known about the salivary composition of the Thysanoptera. Cell-degrading proteins such as amylase, pectinase, cellulase and pectinesterase enable stylet entry into the plant tissue. In contrast, enzymes such as glutathione peroxidase, laccase and trehalase detoxify plant chemicals, enabling the circumvention of plant-defence mechanisms. Salivary enzymes such as M1-zinc metalloprotease and CLIP-domain serine protease as in Acyrthosiphon pisum (Aphididae), and non-enzymatic proteins such as apolipophorin, ficolin-3-like protein and 'lava-lamp' protein as in Diuraphis noxia (Aphididae) have the capacity to alter host-plant-defence mechanisms. A majority of the hemipteroids feed on phloem, hence Ca++-binding proteins such as C002 protein, calreticulin-like isoform 1 and calmodulin (critical for preventing sieve-plate occlusion) are increasingly being recognized in hemipteroid-plant interactions. Determination of a staggering variety of proteins shows the complexity of hemipteroid saliva: effector proteins localized in hemipteran saliva suggest a similarity to the physiology of pathogen-plant interactions.

Study on the physico chemical properties of water of Mouri River, Khulna, Bangladesh

Water sample were collected from six different point of the Mouri River Khulna, Bangladesh with a regular intervals in the months of January-March 2002 for the analyzing different physicochemical parameters of the water. Total 22 different physicochemical parameters were investigated. Correlation and the t value among the parameters were also determined. In the present investigation the minimum and maximum value of water temperature, Transparency, Turbidity, TSS, TDS, Electric Conductivity, water pH, dissolve oxygen, free Carbon dioxide, Alkalinity, Acidity, Hardness, BOD, COD, Sulphate, Phosphate, Nitrite, Sodium, Calcium, Potassium, Manganese and Iron were noted as 21.6 and 32.2 degrees C; 15 and 66 cm; 16 and 22 NTU; 74 and 125 mg L(-1); 255 and 305 mg L(-1); 159 and 275 microS cm(-1); 1.10 mg L(-1) 8.18 mg L(-1); 7.5 and 8.3; 1.1 and 8.3 mg L(-1); 27.5 and 35.5 mg L(-1); 350 and 610 mg L(-1); 32.4 and 171 mg L(-1); 310 and 529 mg L(-1); 13 and 31 mg L(-1); 290 and 365 mg L(-1); 42046 and 57.35 mg L(-1); 4.89 and 11.46 mg L(-1); 0.54 and 1.82 mg L(-1); 16.8 and 33.9 mg L(-1); 1.5 and 6.9 mg L(-1); 49 and 94 mg L(-1); 31 and 59 mg L(-1); 2.6 and 3.8 mg L(-1), respectively. River water did not show any significant pollution during the present study. During the study period dissolved oxygen show direct relation with water temperature but inverse with BOD and COD.

Biochemical composition of some small indigenous fresh water fishes from the River Mouri, Khulna, Bangladesh

Biochemical composition of seven small indigenous fresh water fishes namely Magur (Clarias batrachus), Shingi (Heteropneustes fossilis), Koi (Anabas testudineus), Foli (Notopterus notopterus), Royna (Nandas nandas), Taki (Channa punctatus) and Tangra (Mystus vittatus) from the Mouri river Khulna, Bangladesh was studied in order to evaluate their nutritional values. The mean value of protein, fat, moisture and ash content was found as 14.87 +/- 0.63, 7.90 +/- 1.91, 73.49 +/- 0.69 and 3.74 +/- 0.46% in C. batrachus; 17.34 +/- 0.51, 3.45 +/- 0.92, 76.06 +/- 2.24 and 3.15 +/- 0.25% in H. fossilis; 19.63 +/- 0.5, 7.79 +/- 2.73, 69.27 +/- 1.04 and 3.31 +/- 0.83% in A. testudineus; 18.30 +/- 0.79, 4.98 +/- 1.71, 72.68 +/- 1.08 and 5.82 +/- 0.82% in N. notopterus; 16.09 +/- 2.66, 7.34 +/- 0.49, 75.75 +/- 0.78 and 5.19 +/- .029% in N. nandas; 19.13 +/- 2.40, 4.55 +/- 1.18, 70.55 +/- 1.89 and 6.81 +/- 0.94% in C. punctatus and 15.62 +/- 0.32, 7.53 +/- 1.10, 73.99 +/- 3.13 and 6.50 +/- 0.63% in M. vittatus. Considering the result of the present study, it can be concluded that all the species are rich in food value.

Ethical review of health research: a perspective from developing country researchers

BACKGROUND

Increasing collaboration between industrialised and developing countries in human research studies has led to concerns regarding the potential exploitation of resource deprived countries. This study, commissioned by the former National Bioethics Advisory Commission of the United States, surveyed developing country researchers about their concerns and opinions regarding ethical review processes and the performance of developing country and US international review boards (IRBs).

METHODS

Contact lists from four international organisations were used to identify and survey 670 health researchers in developing countries. A questionnaire with 169 questions explored issues of IRB review, informed consent, and recommendations.

RESULTS

The majority of the developing country researchers were middle aged males who were physicians and were employed by educational institutions, carrying out research on part time basis. Forty four percent of the respondents reported that their studies were not reviewed by a developing country IRB or Ministry of Health and one third of these studies were funded by the US. During the review process issues such as the need for local language consent forms and letters for approval, and confidentiality protection of participants were raised by US IRBs in significantly higher proportions than by host country IRBs.

CONCLUSION

This survey indicates the need for the ethical review of collaborative research in both US and host countries. It also reflects a desire for focused capacity development in supporting ethical review of research.

Skull base involvement by a nasopharyngeal carcinoma shown by Tc-99m MDP SPECT but not by computed tomography

PURPOSE

Plain radiographs, computed tomography (CT), and more recently magnetic resonance imaging (MRI) are used routinely to stage carcinoma of the nasopharynx. Tc-99m methylene diphosphonate (MDP) SPECT is seldom used for local staging of the disease.

MATERIALS AND METHODS

Plain radiographs and CT were used to stage squamous carcinoma of the nasopharynx in a 50-year-old man with a left XII nerve palsy.

RESULTS

Findings of the plain radiographs were normal, whereas the CT scan revealed a nonhomogenous hyperdense mass in the nasopharynx but intact underlying bone. Given the symptoms, a Tc-99m MDP planar scan was ordered and showed no enhanced uptake, but SPECT images obtained at the same time revealed markedly increased focal radiotracer uptake in the region of the tumor, indicating osseous involvement.

CONCLUSION

Possible bony invasion with a nasopharyngeal carcinoma may be better shown with MDP SPECT than with planar isotope bone scans, plain radiographs, or CT.

Prenatal sonographic diagnosis of Neu-Laxova syndrome

We report the sonographic diagnosis of Neu-Laxova syndrome in a fetus at 27 weeks' menstrual age. The parents were first cousins. Sonography revealed microcephaly, a sloping forehead, exophthalmos, a small thorax and abdomen, hypoplastic lungs, syndactyly, hyperextended knees, polyhydramnios, a small placenta, and intrauterine growth restriction. The long bones were normal. The calvaria was hyperechoic and associated with shadowing, obscuring any intracranial abnormalities. This sonographic finding was presumed to represent calvarial calcification, not previously described with this syndrome. We believe that Neu-Laxova syndrome can be reliably diagnosed prenatally by demonstrating the sonographic features described, although other conditions with similar sonographic features need to be considered in the differential diagnosis.

Sonographic diagnosis and follow-up of idiopathic hepatic artery aneurysm, an unusual cause of obstructive jaundice

Hepatic artery aneurysms are rare. We report an idiopathic hepatic artery aneurysm causing obstructive jaundice in a case in which the common hepatic artery arose from the superior mesenteric artery. The diagnosis of hepatic artery aneurysm was suggested by gray-scale sonography, which showed that the common bile duct and intrahepatic biliary radicles were dilated with no obvious intraluminal abnormality and showed no evidence of a mass in the head of the pancreas. A papillotomy of the papilla duodeni major was performed to relieve the cholestasis. Repeat sonography 2 weeks later showed dilatation of the common bile duct and a cyst-like lesion at the porta hepatis impressing the anterior part of the common bile duct. Doppler sonography confirmed pulsatile flow within the cyst-like lesion. Helical CT showed a well-circumscribed lesion with a density similar to that of the abdominal aorta, and mesenteric angiography showed a 3-cm, smooth aneurysm arising from the common hepatic artery, which originated from the superior mesenteric artery. The aneurysm was successfully treated with transcatheter embolization.

Strike feeding behavior in the muskellunge, Esox masquinongy: contributions of the lateral line and visual sensory systems

The muskellunge, Esox masquinongy, is a predatory esocid fish with well-developed visual and lateral line systems. The purpose of this study was to determine the relative roles of these two sensory modalities in organizing the strike behavior of the animal. Subadult muskellunge were videotaped in a test arena while feeding on fathead minnows (Pimephales promelas). Animals were tested under five conditions: (i) control animals in which the visual and lateral line systems were intact; (ii) animals with lateral line afference suppressed by immersion for 12–24 h in 0.1 mmol l(−1) CoCl2; (iii) animals blinded by bilateral optic nerve transection; (iv) animals that had been unilaterally blinded; and (v) animals in which the lateral line system had been unilaterally denervated. The feeding behavior of the muskellunge consists of two phases: a slow stalk of the prey with minimal body movement followed by an explosive C- or S-start lunge at the prey. Quantitative comparisons of animals in the five test groups indicate that, although vision is used in the initial acquisition of the prey, both vision and the lateral line system play important roles in determining the initiation of the rapid strike. The lateral line system may play a critical role in the final capture of the prey at the end of the strike. In addition, lateral-line-suppressed muskellunge strongly alter their approaches to more distant prey. Bilaterally blinded muskellunge do not stalk their prey, but will lunge only at prey that are at close range. Unilaterally blinded or denervated muskellunge also alter their detection of and approach to prey, attending to a wider region of the intact sensory hemisphere. Our data suggest not only that the visual and lateral line systems play complementary roles in the feeding behavior sequence but also that each system plays a more or less dominant role during consecutive phases of the behavior.

Prescribing practices of consultants at Karachi, Pakistan

OBJECTIVE

To audit the prescribing practices of consultants.

DESIGN

A randomized sample survey of 354 consultants prescription for analysis of some basic parameters as recommended by World Health Organization (WHO).

MAIN OUTCOME MEASURES

To provide feedback to the prescribers for promoting rational drug therapy.

RESULTS

The average number of drugs for prescription were found to be 4.51 and the average daily cost of prescribed drugs was Rs: 133.41. The antimicrobials, vitamins/minerals and injections were over-prescribed. About half of the prescribed drugs were from the National Essential Drugs List of Pakistan (NEDLP) and only a little over 12% were prescribed by their generic names.

CONCLUSIONS

The prescribing practices of the consultants in Karachi are rather liberal and not rational. Overuse of antimicrobials and injections have been observed and there is general tendency of indulging in polypharmacy requiring continued medical education.

Enhanced 99Tc(m)-MIBI SPECT detection of hibernating myocardium following the use of sub-lingual nitroglycerine

The purpose of this study was to assess the feasibility of detecting hibernating myocardium using 99Tc(m)-MIBI SPECT imaging following the use of sublingual glyceryl trinitrate (GTN). Thirty-eight subjects were studied, five asymptomatic and 33 with a history of myocardial ischaemia or myocardial infarction (MI). The study was conducted on two separate days, both at rest, one under controlled basal conditions and the other 20 min following the sublingual administration of GTN. A total of 190 cardiac segments were qualitatively analysed and 72 segments with fixed defects were compared to the study following the use of GTN for evidence of improved radionuclide uptake. Following GTN, 73.6% of fixed segment defects showed no change in uptake, 5.5% showed probable improvement whilst in 20.8% a definite enhanced uptake was demonstrated. In 3.7% of segments, worsening of radionuclide uptake was observed.

Sonographic features of mucinous biliary papillomatosis: case report and review of imaging findings

Because of its indolent course, high recurrence rate, and risk of malignant transformation, mucinous biliary papillomatosis is an important consideration in the differential diagnosis of bile duct obstruction. We report a case of mucinous biliary papillomatosis and review the sonographic and other imaging findings previously reported in the literature. On sonography, these tumors appear as nonshadowing intrabiliary masses that are clearly defined and associated with proximal biliary dilatation. They may be multiple and associated with mucoid sludge. The imaging findings reflect the macroscopic appearance of a doughy papilliferous tumor of a bile duct. Associated findings include cholelithiasis, choledocholithiasis, and gallbladder dysplasia.

"Congealed waterlilly" sign: a new sonographic sign of liver hydatid cyst

The ultrasonographic (US) appearance of hydatid liver disease is well established, but solid cysts have long defied US characterization. We present 23 solid cysts and describe a new feature called the "Congealed waterlilly" sign. As the physical characteristics of the hydatid fluid change from watery to a viscid gel, it becomes echogenic. The intact folds of the germinal layer trapped within the viscid matrix give rise to the appearance of curvilinear structures which no longer move with changing patient posture. Similar findings have been observed in eight medically treated patients. We observed progression from an initial simple cyst to a "floating waterlilly" through to a "congealed waterlilly" in treated patients. The final appearance was indistinguishable from the untreated solid cysts. The congealed waterlilly sign is reliable and strongly suggestive of hydatid cysts.

Low seroconversion with hepatitis B vaccination in peritoneal dialysis patients

OBJECTIVE

To compare seroconversion using hepatitis B vaccine between hemodialysis (HD) and peritoneal dialysis (PD) patients.

DESIGN

Data on PD patients vaccinated were collected retrospectively for the period 1992 to 1995. The data on HD patients were collected prospectively from 1991 to 1994.

SETTING

A university outpatient dialysis center.

PARTICIPANTS

All adult patients who received all four doses of hepatitis B vaccine while on dialysis were included (47 PD and 50 HD patients).

INTERVENTION

Recombinant hepatitis B vaccine (Engerix), 40 micrograms IM was administered at 0, 1, 2, and 6 months.

MAIN OUTCOME MEASURE

Seroconversion was measured after completion of the vaccination series.

RESULTS

74% of the HD patients seroconverted compared to 53% of PD patients (p = 0.03). Older, heavier patients compared to all the other patients had a lower seroconversion rate in both the HD patients (55% vs. 78 %) and PD patients (38% vs. 59%) (p = 0.03).

CONCLUSION

The seroconversion rate to recombinant hepatitis B vaccine is lower in patients on PD than on HD for unclear reasons. Further studies are required to determine the etiology of this difference.

Sonography of hepatobiliary ascariasis

We present the real-time sonographic features of 19 surgically proven cases of hepatobiliary ascariasis, in which ultrasound examination was the primary modality used to achieve the diagnosis. All the patients presented with right upper quadrant abdominal symptoms. There were no false positive diagnoses. The "impacted worm" sign, reported here for the first time, presented in two patients as long curved, tubular, non-shadowing structures with echoluscent cores, in the distribution of the intrahepatic biliary ducts. Both of these patients died soon after surgery indicating poor prognosis in such cases. Two other patients are described in whom macerated round worms were seen as intraluminal, localized, soft tissue masses in the common duct mimicking a cholangiocarcinoma. Thus, biliary ascariasis must be added to the differential diagnosis of an intraluminal bile duct mass in patients from endemic areas.

A new potent inhibitor of horse liver alcohol dehydrogenase: p-methylbenzyl hydroperoxide

A product of p-xylene auto-oxidation, p-methylbenzyl hydroperoxide, acts as a very strong reversible inhibitor of the ethanol dehydrogenating activity of horse liver alcohol dehydrogenase. Concentrations of hydroperoxide as low as that of the enzyme active site (about 10(-8) mol.dm-3) in the assay depresses the activity by 50%. Somewhat less potent is benzyl hydroperoxide (derived from toluene) while the (secondary) hydroperoxide derived from ethylbenzene and tert.butyl hydroperoxide and cumyl hydroperoxide do not inhibit HLAD appreciably.

Detection of early xerophthalmia by impression cytology and rose Bengal staining--a comparative study

Twenty two cases were studied for early detection of Xerophthalmia by impression cytology and Rose Bengal staining. Patients were below 6 years of age and admitted in the paediatric ward of Dhaka Medical College Hospital. Assessment were done by conjunctival impression cytology and staining with 1% Rose Bengal dye. Estimation of serum retinol level was done by HPLC to correlate conjunctival findings with biochemical status. The mean age of the subjects were 3.15 +/- 1.75. Rose Bengal staining was positive in 40% cases and impression cytology was in 60% cases. The mean serum retinol level of the diseased children were 10.5 +/- 3. ug/dl. The sensitivity of Rose Bengal staining was 53.3% and that of impression cytology was 80% in detecting vitamin A deficiency when compared with serum retinol level. The specificity of Rose Bengal staining was 40% and that of impression cytology was 100%. Sensitivity of impression cytology was 100% in patient with retinol level 10 ug/dl.

Hydroperoxidic inhibitor of horse liver alcohol dehydrogenase activity, tightly bound to the enzyme-NAD+ complex, characteristically degrades the coenzyme

The strong inhibition of horse liver alcohol dehydrogenase (HLAD) by p-methylbenzyl hydroperoxide (XyHP) is only transient, XyHP behaves also as a pseudo-substrate of the enzyme and in the presence of NAD+, is degraded by HLAD to (as yet unidentified) non-inhibiting products while the NAD+ is converted to a derivative similar to the "NADX", originally observed in an analogous reaction of HLAD with hydrogen peroxide. The apparent KM for XyHP is approximately 10(4) times smaller than that for H2O2. The catalytic constant kcat for HLAD degradation of XyHP is two orders of magnitude less than that for ethanol dehydrogenation. XyHP inhibits both directions of the alcohol-aldehyde interconversion with equal potency. The first step of the inhibition mechanism is a tight binding of XyHP to the binary HLAD-NAD+ complex.

Detection of inflammatory bowel disease in adults and children: evaluation of a new isotopic technique

The distribution of radioactivity after the oral administration of sucralfate labelled with technetium-99m was studied in 33 patients with Crohn's disease (13 adults, 20 children), 10 with ulcerative colitis (four adults), and 29 controls (23 with upper intestinal disease, four irritable bowel, one hypolactasia, and one malrotation of the gut). Positive scans were obtained in all patients with ulcerative colitis and 29 of 31 with active Crohn's disease. The scans of two patients with inactive Crohn's disease were negative. There were two false negative scans in patients with Crohn's colitis and one false positive scan. Overall, sensitivity was 95% and specificity 97%. Comparison with radiology in 39 patients showed similar distribution of disease in 24 and more extensive disease in 12. The scan was inexpensive, simple to perform, well tolerated, allowed small and large bowel to be visualised simultaneously, and used a lower dose of radiation than barium studies. It may prove useful as a screening test for inflammatory bowel disease and in the serial assessment of disease activity.

Psoas muscle hypertrophy: mechanical cause for "jogger's trots?"

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Technetium 99m-labelled-sucralphate isotope scanning in the detection of peptic ulceration

An isotope scan using sucralphate labelled with technetium-99m has been compared with barium meal in the detection of peptic ulceration in 18 patients with endoscopically proven upper gastrointestinal lesions and eight controls. Gastric (75%) and duodenal (67%) ulcers were detected with identical frequency by isotope scan and barium meal but both were inferior to endoscopy. Structural, non-ulcerated lesions, were not identified by isotope scanning. The scan has potential value in duodenal ulcer disease, the serial assessment of ulcer healing and in paediatric gastroenterology.

The primary role of ultrasound in evaluating right-sided diaphragmatic humps and juxtadiaphragmatic masses: a review of 22 cases

Twenty-two successive patients presenting with localised humps on the right hemidiaphragm or juxtadiaphragmatic masses, as revealed on standard chest radiographs, were submitted for ultrasound examination. These were carried out irrespective of the patient's symptoms. Ultrasonography provided a useful adjunct to conventional chest radiography and accurately defined the extent of diaphragmatic humps and the contents of diaphragmatic herniations and juxtadiaphragmatic masses, clearly defining their relationship to the adjacent organs. In most cases further radiological investigations were unnecessary.

Assessment of chemical tests for faecal occult bleeding and correlation of results with presence or absence of anaemia

Stools from 88 consecutive patients in acute geriatric wards were tested for occult blood by four common commercial methods. The Peroheme and Haemostix tests were found too sensitive for general use, the Okokit and Haemoccult tests being preferable. Positive tests were correlated with anaemia in 27 patients, iron deficiency in 26, iron deficiency anaemia in 15, non-anaemia in 52, non-iron deficiency in 43 and with absence of both in 27. Such testing has been considered unnecessary in anaemic patients without gastrointestinal symptoms.

Value of oblique tomography in tracheal stenosis due to retrosternal goitre

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Iminyl radicals in gas-phase synthesis. II. Formation of a-branched nitriles from cycloalkanone azines

Gas-phase pyrolysis of cyclopentanone and cyclohexanone azines results in the formation of iminyl radicals. These undergo ring cleavage to the ω-cyanoalkyl radicals, which stabilize, by internal hydrogen-atom transfer, to the corresponding α-cyanoalkyl radicals. Fragmentation of the latter yields acrylonitrile and alkyl radicals, which can recombine with the α-cyanoalkyl radicals to form α-alkylated nitriles. The mechanisms involved are discussed with reference to isotopic labellingstudies.

The C6H5N energy surface. III. Isomerization processes and intramolecular trapping in picolylcarbenes

The synthesis is reported of a series of 5-(methyl-2-, -3- and -4- pyridyl)tetrazoles from the corresponding picolinecarbonitriles. These compounds are used as gas phase generators for the corresponding picolylcarbenes at 600�/0.05 mm. The normal isomerization process in arylcarbenes are interrupted in some cases by intramolecular trapping by the methyl groups, resulting in the first reported syntheses of cyclobuta-[b] and -[c]pyridines. The major process competing with this is that of nitrogen-extrusion to give tolylnitrenes, which then undergo ring contraction to form methyl-cyclopentadienecarbonitriles. The relative yields from these and other processes are used to deduce the preferred isomerization pathways in picolylcarbenes. In methyl-2- pyridylcarbenes there is almost exclusive insertion into the 2,3-bond, leading to the tolylnitrenes. The 3- and 4-pyridylcarbenes, however, show a tendency for the carbene centre to oscillate over the 3-, 4- and 5-positions of the ring with slower leakage to the 2-position.

The C6H5N energy surface. V. Isomerization of pyridylcarbenes to phenylnitrene - a 13C-labelling study

5-(2-, 3- and 4-Pyridyl)tetrazoles have been synthesized with a 13C- label at the 5-position and pyrolysed at 500-600� under reduced pressure to generate the corresponding pyridylcarbenes. Analysis of the aniline which results from their isomerization to phenylnitrene has been carried out by pulsed Fourier transform 13C N.M.R. The results show that, although both the cycloperambulatory (CP) and insertion-extrusion (IEP) mechanisms are operative, the latter predominates to a very great extent. As in the case of tolylcarbenes, this result is ascribed to a kinetic effect, i.e. the (largely irreversible) nitrogen extrusion step which generates phenylnitrene. The preferred modes of isomerization in the pyridylcarbenes are discussed.