Proton spin coupling constants in methylcyclopentadienes

Abstract

Abstract-A detailed procedure for analysing the 'H n.m.r. spectraSome cyclopentadiene was present in the mixture of isomeric of two isomeric methylcyclopentadienes, two dimethylcyclomethylcyclopentadienes. Di-and trimethylcyclopentadienes were pentadienes and 3-methylindene is reported. Finite perturbation a gift from Dr V. A. Mironov and used without further purification. INDO calculations are used to discuss the conformational features PROCEDURE FOR THE ANALYSIS OF THEof the long range proton coupling constants.SPIN-spin coupling constants of methyl protons neighCalculations of the spectra were performed by using bouring the conjugated double bonds (e.g. in toluene)the YaMR-1 simulating program.15 The LAME are usually of considerable magnitude.l Thls fact is iterative program,lG modified for a BESM-6 computer, often interpreted as a manifestation of a noticeable was also used at the final stage of the investigation. contribution Of the ?r-e!ectrons in the spin informationThe INDOR response was analysed with a special transfer. Until recently, the appropriate data were only simulating 1NDOR program. The main body of the available for t o l~e n e ,~ ~enta-l,3-dienes,~,~ and methyl-I N DOR program consists of the simulating program naphthalene.5 CYclopentadiene is another important YaM R-1 that calculates the theoretical spectrum by conjugated system and the results of the analysis of using the spin Hamiltonian formalism.17.18 For the 'H n.m.r. spectra of cyclopentadiene and its derivatives systems containing magnetically equivalent groups of have also been reported in the (see also nuclei, the YaMR-1 program applies the 'composite the review, Ref. 8). The signs of the spin coupling particle' technique.lg The Hamiltonian matrix H has a constants in C~H G were recently confirmed by using the block structure, where the larger blocks are submatrices method of partially oriented molecules in a neniatjc H,, which correspond to the eigenvalues of the total phase.' The 'H n.m.r. spectra of two isomeric methylspin angular momentum of the groups of equivalent cyclopentadienes have been analysed by using the nuclei, while the smaller blocks are subsubmatrices H,, simulation program YaMR-1,l" and the results of this which belong to one of the eigenvalues of the spin preliminary analysis were supported by the recent operator F, = 21,. FP INDO calculations of Peat and Reynolds.ll We nowThe INDOR program algorithm consists of the report a detailed procedure for analysing the 'H n.m.r.following. The input data are the number of groups of spectra Of l-methylcyclopentadiene (2) and 2-methylmagnetically equivalent spins, the vector of equivalence, cyclopentadiene (3) by iterative programs. The data the chemical shifts, the coupling constants, the frequency of a complete analysis of the 'H n.m.r. spectra of 1,3-of the simulating monitoring line v, and its effective dimethylcyclopentadiene (4) and a partial analysis of width Av. All calculated transitions are numbered the 1H n.m.r. spectra of 1,4-dimethylcyclopentadiene in the order ...

The D iels‐ A lder Reaction with Maleic Anhydride*Present address, University of Southern California, Los Angeles, California.

“…The thermal cracking of the commercially available methylcyclopentadiene dimer typically results in a mixture of three isomeric products, Figure 2. While the resulting mixture has been identified to include traces of cyclopentadiene (Cp), 1-methylcyclopentadiene (1-MeCp), 2-methylcyclopentadiene (2-MeCp) and 5-methylcyclopentadiene (5-MeCp); [5][6][7] without prior knowledge of possible couplings in cyclopentadiene and its derivatives, the analysis and identification of the products can be challenging at the undergraduate level. Using a combination of double resonance experiments and theoretical calculations, the chemical shifts and coupling constants of the protons in 1-MeCp and 2-MeCp have been determined, albeit with some unresolved multiplicity patterns.…”

“…Using a combination of double resonance experiments and theoretical calculations, the chemical shifts and coupling constants of the protons in 1-MeCp and 2-MeCp have been determined, albeit with some unresolved multiplicity patterns. [7] Another added complexity to the spectra of the mixture is the fact that 5-MeCp often appears as a trace and only rarely as an important fraction during the thermal cracking of the MeCp dimer.…”

Asymmetric Synthesis of the Tricyclooctane Core of Trachylobane Natural Products and Related Terpenoids

“…Although cyclopentadienes are known to undergo isomerization via 1,5-H shifts, the other two dimethyl­cyclo­pentadiene isomers of 11 were not detected in 1 H NMR spectra of aliquots of the reaction mixture. − Reduction of 18 with LiAlH 4 followed by NaIO 4 -mediated cleavage of the resulting diol afforded norbornenone 15 in 69% yield over 2 steps as a 25:1 mixture with the regioisomeric ketone as determined by NMR spectroscopy (Scheme ). , …”