untitled


European	Journal	of	Chemistry	8	(1)	(2017)	33‐41	

	

European	Journal	of	Chemistry	
ISSN	2153‐2249	(Print)	/	ISSN	2153‐2257	(Online)		2017	Atlanta	Publishing	House	LLC	‐	All	rights	reserved	‐	Printed	in	the	USA	

http://dx.doi.org/10.5155/eurjchem.8.1.33-41.1529 

	
	

	

	

European	Journal	of	Chemistry	
Journal	webpage:	www.eurjchem.com	 	

	 	 	

Crystal	structure	of	1‐(4‐hydroxybenzoyl)‐2,7‐dimethoxynaphthalene:	
Contribution	of	classical	and	non‐classical	hydrogen	bonding	interactions	to	
the	molecular	packing	structure	

Akiko	Okamoto	*,	Toyokazu	Muto,	Siqingaowa,	Genta	Takahara	and	Noriyuki	Yonezawa	

Department	of	Organic	and	Polymer	Materials	Chemistry,	Tokyo	University	of	Agriculture	and	Technology,	Tokyo,	184‐8588,	Japan	

*	Corresponding	author	at:	Department	of	Organic	and	Polymer	Materials	Chemistry,	Tokyo	University	of	Agriculture	and	Technology,	Tokyo,	184‐8588,	Japan.		
Tel.:	+81.42.3887601.	Fax:	+81.42.3887291.	E‐mail	address:	aokamoto@cc.tuat.ac.jp	(A.	Okamoto).	

	
	

	 	

	 	 	

ARTICLE	INFORMATION	 	 ABSTRACT	

	
DOI: 10.5155/eurjchem.8.1.33-41.1529	

Received:	26	December	2016	
Accepted:	21	January	2017	
Published	online:	31	March	2017	
Printed:	31	March	2017

 

	 Crystal	 structure	 of	 1‐(4‐hydroxybenzoyl)‐2,7‐dimethoxynaphthalene,	 C19O4H16,	 is
reported	from	the	viewpoint	of	characteristics	in	the	helical	alignments	and	difference
compared	to	the	crystal	structure	of	a	structural	 isomeric	compound.	The	asymmetric
unit	of	title	compound	contains	two	conformers	A	and	B.	Furthermore,	the	molecules	in
crystal	exhibit	atropisomerism	brought	about	by	molecular	stereogenic	axis	of	carbon‐
carbon	bond	between	the	carbonyl	moiety	and	the	naphthalene	ring.	Therefore,	a	pair
of	R‐	 and	 S‐enantiomeric	 molecules	 exists	 for	 each	 conformer.	 The	 two	 pairs	 of	 the
enantiomeric	molecules	are	related	by	 two‐fold	helical	axis	 in	 the	asymmetric	unit	of
P21/c	space	group,	exhibiting	the	number	of	molecules	is	eight,	Z	=	8.	Single	molecular
structure	 of	 title	 compound	 shows	 non‐coplanarly	 accumulated	 aromatic‐rings
structure.	The	molecular	packing	structure	is	mainly	stabilized	non‐classical	hydrogen
bonds	involving	C‐H…O	hydrogen	bonds	and	C‐H…π	ones,	however	O‐H…O=C	classical
hydrogen	bonds	are	solely	 formed	between	same	configured	conformers.	Comparison
with	 the	 spatial	 alignment	 of	 an	 isomeric	 homologue,	 2‐hydroxy‐1‐(4‐methoxy
benzoyl)‐7‐methoxynaphthalene,	 has	 clarified	 that	 substitution	 position	 of	 hydroxy
group	determines	not	only	direction	of	classical	hydrogen	bonds	but	also	total	feature
of	molecular	packing,	 i.e.,	 the	homologous	 compound,	which	has	hydroxy	group	at	2‐
position	of	naphthalene	core	forms	intramolecular	O‐H…O=C	classical	hydrogen	bond,
and	O‐H…OMe	classical	hydrogen	bonds	between	opposite	enantiomeric	 isomers.	The
presence/absence	and	direction	of	the	predominantly	strong	classical	hydrogen	bonds
govern	 balance	 of	 interactions	 of	 other	 less	 effective	 classical	 and	 non‐classical
hydrogen	bonds	in	molecular	packing.	In	homologous	compound,	each	of	non‐classical
hydrogen	 bonds	 between	 same	 signed	 enantiomeric	 isomers	 and	 those	 between
opposite	enantiomeric	isomers	demonstrates	almost	same	distances.	In	title	compound,
both	 types	 of	 non‐classical	 hydrogen	 bonds	 formed	 by	 conformer	 A	 are	 imbalanced.
The	 imbalanced	 non‐classical	 hydrogen	 bonds	 are	 adjusted	 and	 reinforced	 by	 non‐
classical	hydrogen	bonds	between	conformers	A	and	B.	

KEYWORDS	
Helical	structure	
Hydrogen	bonds	
Cooperative	effect	
Crystal	engineering	
Noncovalent	interactions	
X‐ray	single	crystal	structure	

Cite	this:	Eur.	J.	Chem.	2017,	8(1),	33‐41	

	
1.	Introduction	
	

Non‐coplanarly	 accumulated‐aromatic‐rings	 containing	
compounds	such	as	aromatic	ring	assembly	of	binaphthyl	and	
biphenyl	 have	 received	 much	 attention	 from	 wide‐range	 of	
organic	 chemists	 and	 material	 chemists	 as	 useful	 molecular	
building	 block	 [1‐4].	 The	 spatial	 organizations	 of	 aromatic	
rings	 in	 these	 molecules	 are	 fixed	 as	 non‐coplanar	 accumu‐
lation	 mode	 leading	 to	 expression	 of	 enantioselectivity	 and	
regioselectivity	 in	 organic	 reaction.	 On	 the	 other	 hand,	 the	
aromatic	ketone	compounds	bearing	some	restriction	against	
structural	 alteration	 also	 have	 non‐coplanar	 alignment	 of	
aromatic	rings	with	relatively	loose	conformational	fixation	of	
substituents.	Recently,	the	authors	have	found	highly	efficient	
diaroylation	at	peri(1,8)‐positions	of	2,7‐dialkoxynaphthalene	
compounds	[5,6].	peri‐Aroylated	naphthalene	compounds	thus	

obtained	 are	 proved	 to	 have	 non‐coplanarly	 accumulated	
aromatic‐rings‐structure	 in	 crystal,	 i.e.,	 the	 aroyl	 groups	 are	
twistedly	 situated	 to	 the	 naphthalene	 ring	 core	 in	 a	
perpendicular	fashion	[7‐9].	Besides,	the	two	aroyl	groups	are	
ordinarily	 oriented	 in	 an	 opposite	 direction	 with	 a	 few	
exceptional	compounds	bearing	unidirectionally‐aligned	aroyl	
groups	 [10,11].	The	non‐coplanarly	 congested	 aromatic	 rings	
spatial	organization	makes	the	authors	imagine	that	formation	
of	 strong	 π…π	 stacking	 interactions	 should	 be	 restricted.	
Indeed,	 molecules	 of	 peri‐aroylnaphthalene	 compounds	 are	
accumulated	 by	weak	 hydrogen	 bonding	 interactions,	mainly	
of	 non‐classical	 hydrogen	 bonding	 interaction	 category	 in	
crystal.	 In	 the	 molecular	 packing	 of	 peri‐aroylnaphthalene	
compounds,	 four	 kinds	 of	 non‐covalent‐bonding	 interactions,	
(sp2)C‐H···O=C	hydrogen	bond,	(sp3)C‐H···O	hydrogen	bond,	C‐
H···π		hydrogen‐bonding		interaction,		and		π···π		stacking		are		



34	 Okamoto	et	al.	/	European	Journal	of	Chemistry	8	(1)	(2017)	33‐41	
	
	
Table	1.	Crystallographic	data	and	structure	refinement	parameters.	
Crystal	data	 	
Chemical	formula	 C19H16O4
Mr		 308.32
Crystal	shape,	colour	 Platelet,	colourless
Crystal	system,	space	group	 Monoclinic,	P21/c
Temperature	(K)	 193.0
a	(Å)	 7.88320	(10)
b	(Å)	 15.9187	(3)
c	(Å)	 24.6606	(4)	
β	(°)	 92.6120	(10)	
V	(Å3)	 3091.45	(9)
Z	 8	
Radiation	type	 CuKα	
µ	(mm−1)	 0.76
Crystal	size	(mm)	 0.50 ×	0.20 ×	0.10
Data	collection	
Diffractometer	 Rigaku	R‐AXIS	RAPID	diffractometer
Absorption	correction	 Numerical NUMABS
Tmin,	Tmax	 0.703,	0.928
No.	of	measured,	independent	and	observed	[I	>	2σ(I)]	reflections 56413,	5667,	4390
Rint	 0.049	
(sin	θ/λ)max	(Å−1)	 0.602	
Refinement	 	
R[F2	>	2σ(F2)],	wR(F2),	S	 0.043,	0.130,	1.02
No.	of	reflections	 5667
No.	of	parameters	 422
H‐atom	treatment	 H‐atom	parameters	constrained
Δρmax,	Δρmin	(e	Å−3)	 0.18,	‐0.17
CCDC	no.	 1520592

	
	
observed	 in	 decreasing	 order	 of	 frequency	 [12].	 In	 solution,	
various	 conformations	 of	 aroyl	 groups	 in	 peri‐aroylnaph‐
thalene	 compounds	 are	 formed	 around	 the	 carbon–carbon	
bond	 between	 the	 carbonyl	 group	 and	 the	 naphthalene	 ring	
[13].	 In	 this	 regard,	 the	 expected	 flexibility	 of	 the	 aromatic	
ketone	 compound	 probably	 shows	 great	 variation	 in	 single	
molecular	 and	 packing	 structures	 in	 the	 crystal.	 Such	 a	
situation	 offers	 a	 good	 opportunity	 to	 reveal	 the	 hitherto	
unclarified	 interactions	 that	 determine	 the	 spatial	 organi‐
zation	 of	 aromatic	 rings	 accumulated	 molecules	 in	 the	
crystalline	state.	This	article	reports	the	synthesis	and	crystal	
structure	of	the	1‐(4‐hydroxybenzoyl)‐2,7‐dimethoxynaphtha‐
lene.	Furthermore,	the	correlation	among	the	single	molecular	
structure,	 the	 non‐covalent	 bonding	 interactions,	 and	 the	
molecular	 packing	 is	 discussed	 through	 comparison	 of	 the	
structural	 isomer,	 2‐hydroxy‐1‐(4‐methoxybenzoyl)‐7‐met‐
hoxynaphthalene	[14].		
	
2.	Experimental	
	
2.1.	Materials	and	methods	
	

All	reagents	were	of	commercial	quality	and	were	used	as	
received.	 Solvents	 were	 dried	 and	 purified	 using	 standard	
procedures	 [15].	 Synthetic	methods	 and	 spectral	 data	 for	 2‐
hydroxy‐1‐(4‐methoxybenzoyl)‐7‐methoxynaphthalene	 [14]	
and	1‐(4‐fluorobenzoyl)‐2,7‐dimethoxynaphthalene	 [16]	have	
been	reported	in	literatures.	

	
2.2.	Measurements	
	

1H	 NMR	 spectra	 were	 recorded	 on	 a	 JEOL	 JNM‐AL300	
spectrometer	(300	MHz)	or	a	JEOL	ECX400	spectrometer	(400	
MHz).	Chemical	shifts	are	expressed	in	ppm	relative	to	internal	
standard	of	Me4Si	(δ,	0.00).	13C	NMR	spectra	were	recorded	on	
a	 JEOL	ECX400	 spectrometer	 (100	MHz).	 Chemical	 shifts	 are	
expressed	 in	 ppm	 relative	 to	 internal	 standard	 of	 CDCl3	 (δ,	
77.0).	 IR	 spectra	 were	 recorded	 on	 a	 JASCO	 FT/IR‐4100	
spectrometer	 (KBr	 tablet).	 Elemental	 analyses	 were	 perfor‐
med	on	a	Yanaco	CHN	CORDER	MT‐5	analyzer.	

	
	
	

2.3.	X‐ray	crystallography	
	

For	 the	crystal	structure	determination,	 the	single‐crystal	
of	title	compound	was	used	for	data	collection	on	a	four‐circle	
Rigaku	 RAXIS	 RAPID	 diffractometer	 (equipped	 with	 a	 two‐
dimensional	area	 IP	detector).	The	graphite‐mono‐chromated	
CuKα	 radiation	 (λ	=	1.54187	Å)	was	used	 for	data	 collection.	
The	 lattice	parameters	were	determined	by	 the	 least‐squares	
methods	on	the	basis	of	all	reflections	with	F2	>	2θ	(F2).		

Crystal	 data,	 data	 collection	 and	 structure	 refinement	
details	 are	 summarized	 in	 Table	 1.	 All	 H	 atoms	 could	 be	
located	 in	 difference	 Fourier	 maps,	 but	 were	 subsequently	
refined	in	optimized	positions	as	riding	atoms,	with	C‐H	=	0.95	
(aromatic)	and	0.98	(methyl)	and	with	Uiso(H)	=	1.2	Ueq(C).	For	
data	 collection:	 PROCESS‐AUTO	 [17];	 cell	 refinement:	
PROCESS‐AUTO	 [17];	 data	 reduction:	 CrystalStructure	 [18];	
program(s)	used	to	solve	structure:	SIR2004	[19];	program(s)	
used	 to	 refine	 structure:	 SHELXL97	 [20];	molecular	 graphics:	
ORTEPIII	 [21].	 The	 hydrogen	 bond	 geometries	 of	 title	
compound	are	listed	in	Table	2.	
	
2.4.	Synthesis	of	title	compound	
	

To	a	10	mL	flask,	1‐(4‐fluorobenzoyl)‐2,7‐dimethoxynaph‐
thalene	(0.20	mmol,	62	mg),	sodium	hydroxide	(1.0	mmol,	40	
mg),	dimethyl	sulfoxide	(0.38	mL),	and	water	(0.13	mL)	were	
placed	 and	 stirred	 at	 120	 °C	 for	 12	h.	 After	 the	 reaction,	 the	
mixture	 was	 poured	 into	 ice‐cooled	 water.	 The	 aqueous	
solution	 was	 acidified	 with	 hydrochloric	 acid	 to	 give	 cake.	
Slightly	yellow	precipitates	thus	obtained	were	collected	with	
suction	 filtration.	 The	 crude	 product	 was	 purified	 by	
recrystallization	from	ethanol.	

1‐(4‐Hydroxybenzoyl)‐2,7‐dimethoxynaphthalene:	 Color:	
Colourless.	Yield:	65%.	M.p.:	180‐182	°C.	FT‐IR	(KBr,	,	cm‐1):	
3367	(OH)	(br,	alcohol),	1642	(C=O)	(ketone),	1626	(Ar),	1602	
(Ar),	 1575	 (Ar),	 1514	 (Ar),	 1277	 (Ar‐O‐CH3),	 1251	 (ArC‐OH),	
1087	 (ArC‐O‐CH3),	 1049	 (ArC‐O‐CH3).	 1H	 NMR	 (300	 MHz,	
CDCl3,	δ,	ppm):	3.69	(s,	3H,	OCH3),	3.79	(s,	3H,	OCH3),	6.40	(br,	
1H,	OH),	6.74	(d,	J	=	2.1	Hz,	1H,	naphthalene‐H),	6.80	(d,	J	=	8.7	
Hz,		2H,		Ar‐H),		7.00		(dd,		J	=	2.4,		9.0		Hz,		1H,		naphthalene‐H),		

	
	

	



Okamoto	et	al.	/	European	Journal	of	Chemistry	8	(1)	(2017)	33‐41	 35	
 

	
Table	2.	Hydrogen	bond	geometry	(Å,	°).	
Hydrogen	bond	 D‐H	 H···A	 D…A	 D—H···A	
O4‐H39…O1	i	 0.84	 1.94 2.7661(15) 170	
O8‐H40…O5	i	 0.84	 1.92 2.7402(17) 165	
C14‐H14…O1	i	 0.95	 2.44 3.1402(18) 131	
C7‐H7…O4	ii	 0.95	 2.62 3.382(2) 138	
C33‐H33…O5	i	 0.95	 2.50	 3.1650(19)	 127	
C35‐H35…O3	iii	 0.95	 2.57	 3.4710(19)	 159	
C37‐H37C…O1	iv	 0.98	 2.58 3.487(2) 154	
C18‐H18B…Cg	v	 0.98	 2.71	 3.3574(18)	 124	
C26‐H26…Cg	vi	 0.95	 2.83	 3.7463(18)	 163	
C4‐H4…Cg	i	 0.95	 2.90 3.4072(18) 115	
C19‐H19B…Cg	vii	 0.98	 2.80 3.7336(18) 159	
Symmetry	codes:	(i)	‐1+x,	y,	z;	(ii)	‐x,	‐1/2+y,	1/2‐z;	(iii)	x,	1/2‐y,	1/2+z;	(iv)	1‐x,	1‐y,	1‐z;	(v)	‐x,	1‐y,	1‐z;	(vi)	1‐x,	‐1/2+y,	1/2‐z;	(vii)	1‐x,	1/2+y,	1/2‐z.		
	
	

Conformer	A	 Conformer	B	

Figure	1.	Molecular	structures	of	conformers	A	and	B	with	displacement	ellipsoids	at	50%	probability.	
	
	
7.14	(d,	J	=	9.0	Hz,	1H,	naphthalene‐H),	7.70	(d,	J	=	9.0	Hz,	1H,	
naphthalene‐H),	7.75	(d,	J	=	8.7	Hz,	2H,	Ar‐H),	7.83	(d,	 J	=	9.0	
Hz,	1H,	naphthalene‐H).	13C	NMR	(75	MHz,	DMSO‐d6,	δ,	ppm):	
194.863	(1C,	C=O),	162.613	(1C,	Ar‐C‐OMe),	158.114	(1C,	Ar‐
C‐OMe),	 154.133	 (1C,	 Ar‐C‐OH),	 132.210	 (1C,	 Ar‐C),	 131.691	
(1C,	 Ar‐C),	 130.479	 (2C,	 Ar‐C),	 129.902	 (1C,	 Ar‐C),	 129.111	
(1C,	 Ar‐C),	 123.804	 (1C,	 Ar‐C),	 121.537	 (1C,	 Ar‐C),	 116.098	
(2C,	 Ar‐C),	 115.488	 (1C,	 Ar‐C),	 110.856	 (1C,	 Ar‐C),	 101.955	
(1C,	Ar‐C),	56.074	 (1C,	OCH3),	54.838	 (1C,	OCH3).	Anal.	 calcd.	
for	C19H1604:	C,	74.01;	H,	5.23.	Found:	C,	74.10;	H,	5.21%.	
	
3.	Results	and	discussion		
	

The	authors	report	crystal	structure	of	title	compound,	1‐
(4‐hydroxybenzoyl)‐2,7‐dimethoxynaphthalene	 especially	
focusing	 on	 helical	 alignments	 of	 the	 molecules	 with	 the	
structural	 difference	 of	 two	 conformers	 both	 in	 single	
molecular	 organization	 and	 in	 accumulation	 feature.	 In	 title	
compound	 molecule,	 the	 4‐hydroxybenzoyl	 group	 is	 non‐
coplanarly	situated	against	the	2,7‐dimethoxynaphthalene	ring	
core.	 In	 addition,	 there	 are	 two	 independent	 molecular	
conformational	isomers	for	title	compound,	conformers	A	and	
B	 (Figure	1).	 Furthermore,	 the	 carbon–carbon	bond	between	
the	 carbonyl	 moiety	 and	 the	 naphthalene	 ring	 acts	 as	 a	
stereogenic	 axis	 affording	 atropisomerism	 to	 the	 molecule.	
Both	conformers	have	R‐	and	S‐enantiomeric	forms.	Moreover,	
the	molecules	are	aligned	forming	21	helical	structure	along	b‐
axis.	Therefore,	 two	pairs	of	R‐	and	S‐enantiomeric	molecules	
exist	 for	both	conformers	 in	 the	asymmetric	units,	which	are	
positioned	 in	 21	 helical	 crystal	 circumstance,	 giving	 Z	 =	 8	
(Figure	 2).	 Two	 conformers	 show	 rather	 small	 difference	 in	
spatial	organization	of	single	molecular	structure.	 Interplanar	
angles	between	benzene	ring	and	naphthalene	ring	for	confor‐
mers	A	and	B	are	69.86°	(O=C‐C‐C	torsion	angle	=	‐63.59°)	and	
72.12°	(O=C‐C‐C	torsion	angle	=	67.77°),	respectively.	In	mole‐

cular	 packing	 of	 title	 compound,	 R‐	 and	 S‐enantiomeric	
isomers	for	each	conformer	form	a	molecular	assembly	with	a	
two‐fold	screw	mode	along	b‐axis.	The	21	helical	assembly	can	
be	differentiated	as	right‐handedness	or	 left‐handedness,	and	
also	as	upwardness	or	downwardness	[22‐25].	Conformers	A	
and	 B	 show	 same	 correlation	 between	 the	 absolute	
configuration	 of	 the	 molecule	 and	 the	 handedness	 and	 the	
orientation	of	the	21	helical	assembly	(Figure	3;	conformer	A:	
green‐colored;	conformer	B:	blue‐colored).	S(R)‐Enantiomeric	
molecules	 form	 right	 (left)‐handed	 and	 downward	 (upward)	
21	helical	assembly.	The	right‐handed	21	helical	assemblies	of	
conformer	 A	 are	 alternately	 arranged	 with	 the	 left‐handed	
ones	 in	 an	 opposite	 orientation	 along	 c‐axis	 (Figure	 4).	
Furthermore,	 the	 right(left)‐handed	 21	 helical	 assemblies	 of	
conformer	 A	 are	 alternately	 stacked	 with	 left(right)‐handed	
ones	 of	 conformer	 B	 in	 an	 opposite	 orientation	 along	 a‐axis	
(Figure	4).		
	

	
	
Figure	2.	Molecular	packing	structure	of	title	compound.	Conformer	A	and	B	
are	expressed	as	green	and	blue,	respectively.	



36	 Okamoto	et	al.	/	European	Journal	of	Chemistry	8	(1)	(2017)	33‐41	
	

(a)	
	

(b)	
	

	(c)	
	
Figure	3.	Correlation	between	 absolute	 configuration	 of	molecule	 and	 the	
handedness	and	the	orientation	of	21	helical	assemblies	in	conformer	A	(a)	
and	 conformer	 B	 (b),	 and	 arrangements	 of	 21	 helical	 assemblies	 of	 two	
conformers	(c).	

	
For	conformer	A	of	title	compound,	 there	are	no	effective	

interactions	 along	 the	 direction	 of	 b‐axis	 among	 S(R)‐
enantiomeric	 molecules	 in	 a	 right(left)‐handed	 21	 helical	
assembly.	 The	 right(left)‐handed	 21	 helical	 assemblies	
composed	of	S(R)‐enantiomeric	molecules	of	conformer	A	are	
connected	 to	 each	 other	 via	 O‐H…O=C	 classical	 hydrogen	
bonds	 [O4‐H39…O1	=	 1.94	Å]	 and	 two	 kinds	 of	 non‐classical	
hydrogen	bonds,	{benzoyl}(sp2)C‐H…O=C	[C14‐H14…O1	=	2.44	
Å]	 and	 {naph}(sp2)C‐H…OH	 hydrogen	 bonds	 [C7‐H7…O4	 =	
2.62	Å]	along	a‐axis	(Figure	5,	left).	The	right‐handed	21	helical	
assemblies	 composed	 of	 S‐enantiomeric	 molecules	 of	
conformer	A	are	linked	with	the	left‐handed	one	composed	of	
R‐enantiomeric	 molecules	 of	 conformer	 A	 by	 {naph}OC‐
H(sp3)…π	non‐classical	hydrogen	bonds	(C18‐H18B…Cg	=	2.71	
Å)	 along	 c‐axis	 (Figure	 5,	 right).	 In	 the	 case	 of	 conformer	 B,	
R(S)‐enantiomeric	 molecules	 forming	 left(right)‐handed	 21	

helical	 assembly	 along	 b‐axis	 have	 no	 effective	 non‐covalent	
bonding	interactions	along	the	direction	of	b‐axis	to	each	other	
as	observed	in	the	21	helical	structure	composed	of	conformer	
A.	 The	 left(right)‐handed	 21	 helical	 assemblies	 composed	 of	
R(S)‐enantiomeric	molecules	of	conformer	B	are	connected	to	
each	other	along	a‐axis	by	O‐H…O=C	classical	hydrogen	bonds	
[O8‐H40…O5	 =	 1.92	 Å]	 and	 {benzoyl}(sp2)C‐H…O=C	 non‐
classical	 hydrogen	 bond	 [C33‐H33…O5	 =	 2.50	 Å]	 as	 same	 as	
the	 interactions	 among	 conformers	 A	 (Figure	 6).	 However,	
there	 are	 no	 effective	 non‐covalent	 bonding	 interactions	
between	 the	 left‐handed	 21	 helical	 assemblies	 and	 the	 right‐
handed	21	helical	 ones	 along	 c‐axis,	 in	 contrast	 to	 the	helical	
structure	of	conformer	A.	This	means	that	conformers	B	form	
effective	 hydrogen	 bonding	 interactions	 mainly	 with	
conformers	A.	The	S(R)‐enantiomeric	molecules	of	conformer	
B	are	connected	to	S(R)‐enantiomeric	molecules	of	conformer	
A	 in	 a	 head‐to‐tail	 fashion	 by	 two	 kinds	 of	 non‐classical	
hydrogen	 bonds,	 {(B)benzoyl}(sp2)C‐H…OMe(A)	 and	 {(B)	
naph}OC‐H(sp3)…O=C(A)	 hydrogen	 bonds	 [C35‐H35…O3	 =	
2.57	 Å	 and	 C37‐H37C…O1	 =	 2.58	 Å]	 along	 c‐axis	 (Figure	 7,	
left).	 The	 R(S)‐enantiomeric	 molecules	 of	 conformer	 B	 are	
linked	to	the	S(R)‐enantiomeric	molecules	of	conformer	A	with	
two	 types	 of	 non‐classical	 C‐H…π	 hydrogen	 bonds,	 head‐to‐
tail‐typed	{(B)naph}(sp2)C‐H…π	{benzoyl(A)}	hydrogen	bonds	
[C26‐H26…Cg	=	2.83	Å],	and	tail‐to‐tail‐typed	{(A)naph}(sp2)C‐
H…π{naph(B)}	 and	 {(A)naph}(sp3)OC‐H…π{naph(B)}[C4‐
H4…Cg	 =	 2.90	 Å	 and	 C19‐H19B…Cg	 =	 2.80	 Å]	 along	 b‐axis	
(Figure	7,	right).	These	results	can	be	interpreted	that	confor‐
mers	 B	 are	 situated	 to	 reinforce	 the	 molecular	 alignment	 of	
conformer	A.		

	

	
	

Figure	4.	Molecular	packing	structure	of	title	compound	viewed	down	three	
directions.	

	
Recently,	 the	authors	have	reported	crystal	 structure	of	a	

structural	isomer	of	title	compound,	2‐hydroxy‐1‐(4‐methoxy‐
benzoyl)‐7‐methoxynaphthalene	(Figure	8)	[14].	There	is	only	
small	 difference	 in	 molecular	 structure	 between	 title	
compound	and	the	homologous	compound,	i.e.,	position	of	the	
hydroxy	group.	The	hydroxy	group	is	situated	at	p‐position	(4‐
position)	of	the	benzoyl	group	in	title	compound,	whereas	that	
is	 attached	 to	 2‐position	 of	 the	 naphthalene	 ring	 in	 the	
homologous	 compound.	 The	 homologous	 compound	 has	 no	
conformers	 in	 the	 crystal.	 The	 intramolecular	 O‐H…O=C	
hydrogen	 bonding	 of	 the	 hydroxy	 group	 at	 2‐position	 of	 the	
naphthalene	 ring	 to	 the	 neighbouring	 carbonyl	 group	 is	
observed	 [1.79	 Å].	 Consequence	 of	 this,	 the	 dihedral	 angle	
between	 bridged	 C‐(C=O)‐C	 plane	 and	 naphthalene	 ring	 is	
smaller	 than	 the	 corresponding	 dihedral	 angle	 of	 title	
compound	 [41.23	 °	 vs.	 64.32	 °	 (Conformer	 A)	 and	 67.55	 °	
(Conformer	 B)].	 In	 a	 similar	 manner	 to	 title	 compound,	 the	
homologous	molecules	 form	 21	 helical	 assembly	with	 a	 two‐
fold	axis	along	b‐axis	in	the	crystal	packing	structure.		

	



Okamoto	et	al.	/	European	Journal	of	Chemistry	8	(1)	(2017)	33‐41	 37	
 

	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
Figure	5.	Hydrogen	bonds	of	conformers	A	 in	crystal	of	 title	compound:	hydrogen	bonds	between	same	enantiomeric	molecules	 (left)	and	hydrogen	bonds	
between	opposite‐enantiomeric	molecules	(right).	
	
	

	
	

Figure	6.	Hydrogen	bonds	of	conformers	B	in	crystal	of	title	compound:	hydrogen	bonds	between	same	enantiomeric	molecules.	
	
	
However,	 the	 correlation	 between	 the	 absolute	

configuration	 of	 the	 molecule	 and	 the	 handedness	 of	 the	 21	
helical	 assembly	 is	 inversely	 related	 to	 title	 compound,	 i.e.,	
S(R)‐enantiomeric	molecules	form	left(right)‐handed	21	helical	
assembly	 (Figure	 9,	 S‐enantiomeric	 isomers	 and	 R‐enantio‐
meric	 isomers	 are	 expressed	 as	 pink‐colored	 molecules	 and	
pale	blue‐colored	molecules,	 respectively).	Both	right‐handed	
and	left‐handed	21	helical	assemblies	are	oriented	in	upward.	
Left(Right)‐handed	21	 helical	 assemblies	 are	 aligned	 along	a‐

axis,	 and	 are	 alternately	 arranged	 with	 right(left)‐handed	 21	
helical	 assemblies	 along	 c‐axis	 in	 same	 orientation.	 S(R)‐
enantiomeric	 molecules	 of	 the	 homologous	 compound	 are	
linked	 to	 each	 other	 through	 {benzoyl}OC‐H(sp3)…π{naph}	
non‐classical	 hydrogen	 bond	 [2.82	 Å]	 forming	 left(right)‐
handed	21	helical	assembly	along	b‐axis	 (Figure	10,	 left).	The	
left(right)‐handed	 21	 helical	 assemblies	 aligned	 along	 a‐axis	
are	 connected	 to	 each	 other	 by	 {naph}(sp2)C‐H…π{benzoyl}	
non‐classical	hydrogen	bonds	[2.81	Å]	(Figure	10,	left).		



38	 Okamoto	et	al.	/	European	Journal	of	Chemistry	8	(1)	(2017)	33‐41	
	

	

	
	
Figure	7.	 Hydrogen	 bonds	 between	 conformers	 A	 and	 conformers	 B	 in	 crystal	 of	 title	 compound:	 hydrogen	 bonds	 between	 S‐enantiomeric	molecules	 of	
conformer	A	and	S‐enantiomeric	molecules	of	conformer	B	(left)	and	hydrogen	bonds	between	S‐enantiomeric	molecules	of	conformer	A	and	R‐enantiomeric	
molecules	of	conformer	B	(right).	
	
	

Figure	8.	Single	molecular	strusture	of	homologous	compound	with	intramolecular	O‐H…O=C	hydrogen	bond	(see	ref.	[14]).	

	
S‐Enantiomeric	 molecules	 of	 the	 left‐handed	 21	 helical	

assemblies	are	 connected	 to	 the	R‐enantiomeric	molecules	of	
the	 right‐handed	 ones	 by	 two	 types	 of	 non‐covalent	 bonding	
interact‐tions	 along	 ac‐diagonal,	 i.e.,	 head‐to‐tail‐typed	 O‐
H…OMe	 {benzoyl}	 classical	 hydrogen	 bond	 [2.55	 Å]	 and	
{benzoyl}	(sp2)C‐H…OH	non‐classical	hydrogen	bond	[2.60	Å],	
and	 tail‐to‐tail(head‐to‐head)‐typed	 {naph}OC‐H(sp3)…π	
{naph}	 non‐classical	 hydrogen	 bonds	 [2.91	 Å]	 (Figure	 10,	
right).		

Non‐covalent	 bonding	 interactions	 of	 title	 molecule	 and	
the	homologous	molecule	are	classified	by	types	and	distances	
as	shown	in	Table	3.	Non‐covalent	bonding	distances	between	
same	 enantiomeric	molecules	 are	 exhibited	with	 red	 charac‐
ters,	and	those	between	opposite‐enantiomeric	molecules	are	
shown	 as	 blue	 characters.	 Besides,	 non‐covalent	 bonding	
distances	between	R(S)‐enantiomeric	molecule	of	conformer	A	
and	R(S)‐enantiomeric	molecule	of	conformer	B	are	expressed	

as	 orange	 characters,	 and	 those	 between	 R(S)‐enantiomeric	
molecule	 of	 conformer	 A	 and	 S(R)‐enantiomeric	 molecule	 of	
conformer	 B	 are	 shown	 as	 purple	 characters.	 As	 common	
features	of	title	compound	and	the	homologous	compound,	O‐
H…O=C	 classical	 hydrogen	 bonds	 are	 observed	 in	 their	
crystals.	 However,	 the	 O‐H…O=C	 classical	 hydrogen	 bond	 in	
homologous	compound	is	intramolecularly	formed.	Individual	
features	 of	 title	 compound	 and	 homologous	 compound	 are	
described	below.	In	homologous	molecule,	O‐H…OMe	classical	
hydrogen	 bonds	 and	 {benzoyl}(sp2)C‐H…OH	 non‐classical	
hydrogen	 bonds	 are	 formed	 between	 opposite‐enantiomeric	
molecules,	 i.e.,	 between	 R‐enantiomeric	 molecule	 and	 S‐
enantiomeric	 one.	 They	 are	 observed	 along	 ac‐diagonal,	 and	
the	distances	are	approximately	 same	 (2.55	and	2.60	Å).	The	
C‐H…π	 non‐classical	 hydrogen	 bonds	 are	 formed	 between	
same	enantiomeric	molecules,	 i.e.,	between	R(S)‐enantiomeric	
molecules.		



Okamoto	et	al.	/	European	Journal	of	Chemistry	8	(1)	(2017)	33‐41	 39	
 

	 	

	
	
Figure	 9.	 Molecular	 packing	 structures	 of	 homologous	 compound	 viewed	 down	 three	 directions:	 R‐enantiomeric	 isomer	 and	 S‐enantiomeric	 isomer	 are	
expressed	as	pale	blue‐colored	molecule	and	pink‐colored	molecule,	respectively.		

	

	
	
Figure	10.	Hydrogen	bonds	in	crystal	of	homologous	compound:	hydrogen	bonds	between	same	enantiomeric	molecules	(left)	and	hydrogen	bonds	between	
opposite‐enantiomeric	molecules	(right).	
	
Table	3.	Non‐covalent	bonding	interactions	in	title	compound	and	the	homologous	compound	(Å)	
Interactions		 Homologue	 Title	compound	

Conformer	A Conformer	B
O‐H…O=C	(Intra)		 1.79	 ‐	 ‐	
O‐H…O=C	 ‐	 1.94	 1.92	
O‐H…OMe{benzoyl}	 2.55	 ‐	 ‐	
{benzoyl}(sp2)C‐H…O=C	 ‐	 2.44	 2.50	
{benzoyl}(sp2)C‐H…OMe	 ‐	 2.57	
{naph}OC‐H(sp3)…O=C	 ‐ 2.58	
{benzoyl}(sp2)C‐H…OH	 2.60	 ‐	 ‐	
{naph}(sp2)C‐H…OH	 ‐	 2.62	 ‐	
{naph}OC‐H(sp3)…	π	{benzoyl}	 ‐ 2.71 ‐	
{naph}OC‐H(sp3)…	π	{naph}	 ‐	 2.80	
{naph}(sp2)C‐H…	π	{naph}	 2.81	 ‐	 ‐	
{benzoyl}OC‐H(sp3)…	π	{naph}	 2.82 ‐ ‐	
{naph}(sp2)C‐H…	π	{benzoyl}	 ‐	 2.83	
{naph}(sp2)C‐H…	π	{naph}	 ‐	 2.90	
{naph}OC‐H(sp3)…	π	{naph}	 2.91 ‐ ‐	
Red	characters	=	Non‐covalent	bonding	distances	between	same	enantiomeric	molecules;	blue	characters	=	non‐covalent	bonding	distances	between	opposite‐
enantiomeric	molecules;	 orange	 characters	 =	 non‐covalent	 bonding	 distances	 between	R(S)‐enantiomeric	molecule	 of	 conformer	 A	 and	R(S)‐enantiomeric	
molecule	 of	 conformer	 B;	 purple	 characters:	 non‐covalent	 bonding	 distances	 between	 R(S)‐enantiomeric	molecule	 of	 conformer	 A	 and	 S(R)‐enantiomeric	
molecule	of	conformer	B.	Under	lines	indicate	that	the	moiety	is	in	conformer	A.	
	

	



40	 Okamoto	et	al.	/	European	Journal	of	Chemistry	8	(1)	(2017)	33‐41	
	

	
They	 are	 observed	 along	 a‐axis,	 and	 the	 distances	 are	

almost	 same	 (2.81	 and	 2.82	 Å).	 On	 the	 other	 hand,	 title	
molecule	 shows	 converse	 relation	 with	 the	 homologous	
molecule	 in	 kinds	 of	 hydrogen	 bonds	 and	 the	 counter	
molecule’s	 absolute	 configuration.	 O‐H…O=C	 Classical	
hydrogen	bonds	and	C‐H…O	non‐classical	hydrogen	bonds	are	
observed	 between	 same	 enantiomeric	 molecules	 (red	
characters).		

The	 C‐H…π	 non‐classical	 hydrogen	 bonds	 are	 formed	
between	 opposite‐enantiomeric	 molecules	 (blue	 characters).	
In	 conformer	 A,	 there	 is	 large	 difference	 in	 the	 non‐covalent	
bonding	 distances	 between	 same	 enantiomeric	 molecules	 as	
classical	 O‐H…O=C	 hydrogen	 bonds	 (1.94	 Å),	 non‐classical	
{benzoyl}(sp2)C‐H…O=C	 hydrogen	 bonds	 (2.44	 Å),	 and	 non‐
classical	 {naph}(sp2)C‐H…OH	 hydrogen	 bonds	 (2.62	 Å).	 The	
gap	 seems	 to	 be	 bridged	 by	 non‐classical	 hydrogen	 bonds	
among	 conformer	 A	 and	 conformer	 B	 (orange	 characters),	
{benzoyl(B)}(sp2)C‐H…OMe(A)	 hydrogen	 bonds	 (2.57	 Å)	 and	
{naph(B)}OC‐H(sp3)…O=C(A)	 hydrogen	 bonds	 (2.58	 Å).	
Conformer	B	 essentially	 plays	 same	 role	 for	 hydrogen	 bonds	
between	 opposite‐enantiomeric	 molecules	 of	 conformer	 A	
(purple	characters).	S‐Enantiomeric	molecules	of	conformer	A	
are	 connected	 with	 R‐enantiomeric	 ones	 of	 conformer	 A	 by	
only	 C‐H…π	 {naph}OC‐H(sp3)…π{benzoyl}	 hydrogen	 bonds	
(2.71	 Å)	 (blue	 characters).	 R‐Enantiomeric	 molecules	 of	
conformer	 B	 seem	 to	 form	 contact	 alignment	 of	 S‐
enantiomeric	ones	of	conformer	A	by	formation	of	three	types	
of	 weak	 C‐H…π	 hydrogen	 bonds	 with	 S‐enantiomeric	
molecules	 of	 conformer	 A	 (purple	 characters),	 {naph(A)}OC‐
H(sp3)…π{naph(B)}	hydrogen	bond	(2.80	Å),	{naph(B)}(sp2)C‐
H…π{benzoyl(A)}	 hydrogen	 bond	 (2.83	 Å),	 and	 {naph(A)}	
(sp2)C‐H…π{naph(B)}	hydrogen	bond	(2.90	Å).		

Direction	of	classical	hydrogen	bonding	interactions	seems	
to	be	related	with	the	spatial	distance	of	hydroxy	group	from	
chiral	axis.		

Classical	 hydrogen	 bonds	 are	 formed	 between	 opposite‐
enantiomeric	 molecules	 when	 hydroxy	 group	 is	 situated	 at	
vicinal	 position	 of	 the	 chiral	 axis	 such	 as	 homologous	
molecule,	 whereas	 those	 are	 formed	 between	 same	 enan‐
tiomeric	molecules	when	 the	hydroxy	group	 is	positioned	 far	
from	 the	 chiral	 axis	 as	 title	 compound.	 The	 direction	 of	
classical	hydrogen	bonds	 influences	 to	balanced	 formation	of	
non‐classical	hydrogen	bonds.	When	classical	hydrogen	bonds	
are	 formed	 between	 opposite‐enantiomeric	 molecules	 as	
shown	 in	 homologous	 compound,	 non‐classical	 hydrogen	
bonds	 between	 same	 enantiomeric	 molecules	 and	 those	
between	 opposite‐enantiomeric	 molecules	 are	 almost	 same	
distances,	 respectively	 (2.81	 and	 2.82	 Å	 for	 non‐classical	
hydrogen	bonds	between	 same	enantiomeric	molecules;	2.55	
and	 2.60	 Å	 for	 non‐classical	 hydrogen	 bonds	 between	
opposite‐enantiomeric	 molecules).	 However,	 non‐classical	
hydrogen	bonds	are	obliged	 to	 take	an	 imbalance	state	when	
classical	 hydrogen	 bonds	 are	 formed	 between	 same	
enantiomeric	 molecules	 as	 shown	 in	 conformer	 A	 of	 title	
compound	(2.44	and	2.62	Å).	The	 independent	molecules	are	
considered	 to	act	an	 intermediate	 to	each	other	 to	adjust	 the	
imbalance	 of	 non‐classical	 hydrogen	bonds	 and	 reinforce	 the	
spatial	packing	of	molecules	together.	
	
4.	Conclusion	
	

Conclusively,	 comparison	 of	 spatial	 organization	 of	 title	
compound	 and	 the	 homologous	 compound	 reveals	 the	
characteristic	relation	between	the	position	of	hydroxy	group	
in	 molecules	 and	 accumulation	 structure	 of	 these	 pairs	 of	
isomeric	 aromatic	 rings	 combination	 compounds.	 Both	
isomeric	 compounds	 have	 sole	 hydroxy	 group	 capable	 for	
forming	 classical	 hydrogen	 bonding.	 The	 position	 of	 the	
hydroxy	 group	 in	 single	molecular	 structure	 determined	 the	
place	 of	 the	 hydrogen	 bondings.	 The	 intermolecular	 classical	

hydrogen	bonding	is	observed	in	both	of	title	compounds	and	
homologous	 one.	 On	 the	 other	 hand,	 intramolecular	 classical	
one	is	confirmed	only	in	homologous	compound.	The	position	
and	 the	 direction	 of	 the	 strongest	 non‐covalent	 bonding	
interaction	are	presumed	to	govern	the	diversity	of	the	crystal	
system	 of	 these	 compounds.	 The	 intermolecular	 classical	
hydrogen	 bonding	 makes	 contact	 alignment	 of	 molecules	 in	
one	 direction,	 which	 bring	 about	 small	 flexibility	 of	
conformation	 of	 molecules	 resulting	 in	 requirement	 of	
assistance	 of	 another	 conformer	 (independent	 molecule)	 to	
achieve	 the	 dense	 packing	 of	 molecules.	 Two	 kinds	 of	
conformers	 with	 enantiomers	 realize	 the	 stable	 crystal	
packing	 cooperatively.	 On	 the	 other	 hand,	 the	 homologous	
compound,	which	 consumes	 the	 strongest	 classical	 hydrogen	
bonding	in	the	core	part	of	molecules,	are	considered	to	make	
most	fitted	conformation	for	rather	depressed	intermolecular	
classical	 hydrogen	 bonding	 and	 other	 non‐classical	 hydrogen	
bondings	 realizing	 favourable	 conformation	 in	 enthalpy	 and	
symmetry,	without	presence	of	independent	molecules.	
	
Acknowledgements	
	

The	 authors	 would	 express	 their	 gratitude	 to	 Professor	
Keiichi	 Noguchi,	 Instrumentation	 Analysis	 Center,	 Tokyo	
University	 of	 Agriculture	 and	 Technology,	 for	 his	 technical	
advice.	 This	work	was	 partially	 supported	 by	 the	Ogasawara	
Foundation	 for	 the	 Promotion	 of	 Science	 &	 Engineering,	
Tokyo,	Japan.	
	
Supplementary	material	
	

All	 crystallographic	 data	 for	 this	 paper	 are	 deposited	 in	
Cambridge	Crystallographic	Data	Centre	(CCDC	1520592).	The	
data	can	be	obtained	free	of	charge	at	www.ccdc.cam.ac.uk	or	
from	Cambridge	Crystallographic	Data	Centre,	12	Union	Road,	
Cambridge	 CB2	 1EZ,	 UK;	 fax	 +44	 (0)	 1223	 336033,	 e‐mail:	
deposit@ccdc.cam.ac.uk.	
	
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