“…-90°. 16 Cyclization affects the HB more than the HA resonances in 13, 14, and 18, while the reverse is true for 15 and 17. We therefore assume that the conformations indicated for 13, 14, and 18 (with both HB internal) are the main contributors to the structures of these compounds but that conformations of type 22 (with both HA internal) are the main contributors to 15 and 17.17 This assumption is supported by the fact that JB,C = -9.5 Hz in 13, 14, and 18, but only 5 Hz in 15, 16, and 17.18 The unusually high field HA resonances in 15, 16, and 17 are presumably due to the anisotropy of the acetylenes, and it appears that such anisotropy can cause either an upfield or a downfield shift, depending on the exact dispositions of the groups.19…”