Table 3. Selected geometrical parameters (Å, °) for the three structural domains of fuco­xanthin.

Parameter/domain	fucoA	fucoB
Allenic cyclo­hexyl end group
Allene C=C	C1—C12 1.308 (3); C12—C13 1.314 (3)	C43—C54 1.300 (3); C54—C55 1.317 (3)
Allene angle	C1—C12—C13 177.3 (2)	C43—C54—C55 178.4 (2)
Acet­oxy C—O /O—C/C=O	C4—O2 1.460 (3); O2—C8 1.352 (3);	C46—O8 1.468 (2); O8—C50 1.336 (3);
	C8—O3 1.199 (3)	C50—O9 1.208 (3)
Conjugated polyene/ketone segment
Mean formal C=C in polyene chain	1.359; range 1.354–1.368	1.358; range 1.355–1.366
Mean inter­vening C—C in polyene chain	1.449; range 1.425–1.484	1.449; range 1.430–1.477
Ketone C=O	C32—O4 1.222 (3)	C74—O10 1.219 (3)
Representative polyene torsion angles	C12—C13—C14—C16 177.9 (2);	C54—C55—C56—C58 −171.5 (2);
	C13—C14—C16—C17 −179.3 (2);	C55—C56—C58—C59 176.8 (2);
	C16—C17—C18—C19 −177.0 (2);	C58—C59—C60—C61 177.5 (2);
	C21—C22—C23—C24 177.6 (2)	C63—C64—C65—C66 −175.7 (2)
5,6-Ep­oxy ionone end group
Epoxide C—O	C34—O5 1.461 (3); C35—O5 1.457 (3)	C76—O11 1.463 (3); C77—O11 1.453 (3)
Epoxide angle	C34—O5—C35 60.90 (14)	C76—O11—C77 60.85 (14)
Hy­droxy C—O	C37—O6 1.430 (3)	C79—O12 1.428 (3)
Terminal-ring junction torsion angles	C30—C32—C33—C34 −163.4 (2);	C72—C74—C75—C76 −179.1 (2);
	C32—C33—C34—C35 −77.8 (3);	C74—C75—C76—C77 −71.3 (3);
	C33—C34—C35—C36 153.8 (2)	C75—C76—C77—C78 153.2 (2)

Note: formal C=C and inter­vening C—C averages were calculated from the crystallographically defined conjugated polyene segment, excluding the allene and the terminal saturated ring bonds.