N.M.R. Studies of Bridged Ring Systems. I. Carbon-Hydrogen Spin Coupling Constants in Bicyclo[2,2,1]heptane Derivatives

Abstract

which mas previously evacuated and weighed. The flask was then filled with dry ether to precipitate the salt and placed in the refrigerator overnight. The liquor was decanted using an aspirator, but enough was left behind to keep the crystals covered. The remaining liquid was removed under vacuum. The white salt was then dried over phosphorous pentoxide under vacuum. a -P h e n e t h~ ldimethylsulphoniurn bromide-reaction time 96hours; yield 10.17,; 1n.p. 91.7-92.8" C (lit. 1n.p. 76-80" C ref. ( 8 ) N.M.R. STUDIES OF BRIDGED RING SYSTEMS. I. CARBON-HYDROGEN SPIN COUPLING CONSTANTS IN BICYCL0[2,2,1]HEPTANE DERIVATIVES K. TORI, R. ~I V N E Y U K I , AND H. TANIDAThe carbon-hydrogen spin coupling constants, J C~3 -H , are considered as useful tools for the investigatio~l of s-character of the carbon atomic orbital participating in the C-H bond (1-4). JIuller and Pritchard ( I ) suggested that decrease of the ring size of cycloalkanes with their C-C-C angles increased JC1sPH with the percentage of scharacter of the C-H bond, and, for example, the JC13-H of c>-clopropane exhibited the comparable value to that of the sp2 bond.I t has been known that bicyclo[2,2,l]heptane derivatives have considerably smaller bond angles on their sp3-tetrahedral and spxtrigonal carbons than the respective ordinal angles due to the contribution of ring strain.* llIusher (7) proposed that the unusual behavior of the bicyclo[2,2,l]heptane ring toward the magnetic shielding and the proton coupling constant might be due to the n-character in the ring.

N.M.R. Studies of Bridged Ring Systems: Ii. Unusual Magnetic Deshielding Effect on the Bridge Methylenes of Norbornadiene and Benzonorbornadiene

“…Additional long-range spin couplings, if they appear, will be small (3, 8,11). The geminal coupling constant of these bridge methylene protons is believed to be about 8 c.p.s., which is unusually small, by reference to this sort of the coupling constant in V (20). The differences in the chemical shifts between the protons H, and H, on the ethylene bridge of I1 and IV should be much larger than the value observed in I , because of the anisotropy effect of a double bond or a benzene ring.…”

“…of C-C bonds of 111 and V with the "bent" of the bonds due to the Inore ring strain, as reflected in the increased JC13-R values in the rings (20). The signal of the bridge methylene of VI also appears a t a very low field as 7.987, as shown in Table I.…”

“…This fact could not be explained by the change of molecular geometries due to the introduction of two T-electron systems. Recently we proposed the increasing of s-character in all the C-H bonds of this ring system (20). Moreover, recent studies of ultraviolet absorption spectroscopy demonstrated a considerably larger transannular interaction between two double bonds of 111, and its resonance integral value was estimated t o be In contrast, the ultraviolet spectrum of VIII suggests that this kind of interaction is not so large as that of I11 (33).…”

The Reactivity of the Cyclic Polyenes Towards Free Radicals: Ii. Metathesis With the Ethyl Radical

“…Nuclear magnetic resonance studies have shown that this bridgehead bond has a much higher degree of s-character than is found in a normal sp3 bond (25). All other hydrogen atoms of the bicycloheptadiene molecule are liltely to show low reactivity towards metathesis, but the double bonds are reactive towards the addition of free radicals in general, and the ethyl radical in particular.…”

The behavior of quantum chemical bond order in the vicinity of a saddle point on the reaction path

“…But the success of BEBO formalism merits further attention. One wonders whether the quantum chemical bond order or some other property of the bond being broken or formed would generally reveal some "exalted" features when examined along the reaction path.30 If the answer (5) Mayer, S. W.; Schieler, L; Johnston, H. Table II. Variation in the Computed Hydrogen Free Valence Index (fH) along the Photodissociation Path of HNO (3A")°- Figure 1 shows the section of the potential energy surface along the reaction path for the isomerization of HNO to NOH in the lowest 3A" state.…”