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European	Journal	of	Chemistry	5	(1)	(2014)	6‐10	

	

European	Journal	of	Chemistry	
ISSN	2153‐2249	(Print)	/	ISSN	2153‐2257	(Online)		2014	Eurjchem	Publishing	‐	Printed	in	the	USA	

http://dx.doi.org/10.5155/eurjchem.5.1.6‐10.933	

	
	

	

	

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

	 	 	

Crystal	structures	of	racemic	and	enantiomeric	5‐isopropyl‐5‐methylhydantoin	

Masaki	Ichitani,	Soh‐ichi	Kitoh,	Keiko	Tanaka,	Shuhei	Fujinami,		
Mitsuhiro	Suda,	Mitsunori	Honda	and	Ko‐Ki	Kunimoto	*	

Graduate	School	of	Natural	Science	and	Technology,	Kanazawa	University,	Kakuma‐machi,	Kanazawa	920‐1192,	Japan	

*Corresponding	author	at:	Graduate	School	of	Natural	Science	and	Technology,	Kanazawa	University,	Kakuma‐machi,	Kanazawa	920‐1192,	Japan.		
Tel.:	+81.76.2646292.	Fax:	+81.76.2646292.	E‐mail	address:	kunimoto@se.kanazawa‐u.ac.jp	(K.‐K.	Kunimoto).	

	
	

	 	

	 	 	
ARTICLE	INFORMATION	 	 ABSTRACT

	
DOI:	10.5155/eurjchem.5.1.6‐10.933	

Received:	25	September	2013	
Accepted:	06	October	2013	
Online:	31	March	2014	

KEYWORDS	

	 Crystal	structures	of	racemic	and	enantiomeric	5‐isopropyl‐5‐methylhydantoin	(IPrMH)	have
been	 determined	 by	 single	 crystal	 X‐ray	 diffraction.	 Melting	 temperatures	 and	 solid	 state
infrared	spectra	are	also	measured.	Racemic	IPrMH	has	a	lower	melting	temperature	than	the
pure	enantiomer	by	25	°C.	The	 infrared	spectrum	of	racemic	 IPrMH	 is	 identical	with	that	of
the	pure	enantiomer.	Nevertheless,	 the	racemic	 IPrMH	doesn’t	crystallize	as	a	conglomerate
but	 as	 a	 racemic	 compound.	 The	 racemic	 and	 the	 enantiomeric	 crystals	 are	 very	 similar	 to
each	 other	 in	molecular	 geometries	 and	 intermolecular	 interactions.	 In	 the	 both	 cases,	 the
molecules	are	connected	via	N−H···O	hydrogen	bonds	to	form	R22(8)	rings,	and	these	rings	are
linked	into	infinite	one‐dimensional	tapes.	In	the	racemic	crystal,	a	single	tape	is	composed	of
single	enantiomer	and	itself	is	homochiral.	

Hydantoin	
Enantiomer	
Conglomerate	
Crystal	structure	
Racemic	compound	
Imidazolidine‐2,4‐dione	

	
1.	Introduction	
	

Hydantoins	 (imidazolidine‐2,4‐diones)	 and	 2‐thiohydan‐
toins	(2‐thioxoimidazolidin‐4‐ones)	are	two	classes	of	5‐mem‐
bered	heterocycles	containing	two	nitrogens	in	an	ureide	and	a	
thioureide	 configuration,	 respectively.	 Due	 to	 their	 diverse	
biological	 and	 pharmacological	 properties,	 these	 compounds	
have	 been	 used	 in	 a	 wide	 variety	 of	 applications	 [1].	 For	
instance,	hydantoins	have	been	widely	used	as	antiarrhythmic	
and	 antihypertensive	 [2,3],	 antiviral	 [4],	 antineoplastic	 [5],	
antitumoral	 [6]	 and	 anticonvulsant	 agents	 [7,8].	 Thiohydan‐
toins	are	known	for	their	uses	as	hypolipidemic	[9],	antimuta‐
genic	 [10]	 and	 anticarcinogenic	 agents	 [11].	 In	 addition,	 both	
compounds	 are	used	 as	herbicides	 [12]	 and	 fungicides	 agents	
[13].	

These	 classes	 of	 compounds	 commonly	 carry	 the	 amide	
and/or	 the	 thioamide	 groups	 in	 a	 molecule,	 which	 provides	
equal	 number	 of	 hydrogen‐bond	 proton	 donor	 (D)	 and	
acceptor	 (A)	 in	 the	 D‐A‐D‐A	 sequence.	 This	 unique	 structural	
feature	 endows	 the	 compounds	 with	 unique	 physicochemical	
and	biological	properties	 [14,15].	We	have	studied	 the	 crystal	
structures	 of	 a	 series	 of	 hydantoins	 and	 2‐thiohydantoins	 in	
order	 to	 get	 information	 on	 the	 factors	 controlling	 the	
molecular	environment	in	the	crystal	[16‐22].	

For	 a	 chiral	 compound,	 the	 racemic	 compound	 and	 the	
enantiomer	 essentially	 possess	 different	 crystal	 structures.	
These	 differences	 in	 crystal	 structures	 lead	 to	 the	 different	

physicochemical	 properties	 of	 the	 racemic	 and	 the	
enantiomeric	compounds.	Thus,	comparison	of	the	racemic	and	
the	enantiomeric	crystal	structures	offers	a	unique	opportunity	
to	 study	 the	 differences	 in	 the	 intermolecular	 interactions	 and	
the	molecular	packings	involving	the	same	molecule	in	different	
crystalline	environments.	

In	 this	 study,	 the	 racemate	 and	 (S)‐enantiomer	 of	 5‐
isopropyl‐5‐methylhydantoin	 ((rac)‐IPrMH)	 and	 (S)‐IPrMH)	
have	been	synthesized	(Figure	1).	These	crystal	structures	are	
analyzed	 by	 the	 single	 crystal	 X‐ray	 diffraction.	 Melting	
temperatures	 and	 solid	 state	 infrared	 (IR)	 spectra	 of	 both	
crystals	are	also	discussed.	
	

		
	

Figure	1.	Chemical	structure	of	5‐isopropyl‐5‐methylhydantoin (IPrMH).
	
2.	Experimental	
	
2.1.	Instrumentation	



Ichitani	et	al.	/	European	Journal	of	Chemistry	5	(1)	(2014)	6‐10	 7	
 

	 	
Table	1.	Crystal	data	and	structure	refinement.	

(rac)‐IPrMH	 (S)‐IPrMH	
Empirical	formula	 C7H12N2O2 C7H12N2O2	
Formula	weight	 156.19 156.19
Temperature	 123(2)	K 123(2)	K	
Wavelength	 0.71070	Å 0.71070	Å	
Crystal	system	 Monoclinic	 Monoclinic	
Space	group	 P21/n	 P21	
Unit	cell	dimensions	 a	=	11.0943(18)	Å a =	6.8048(12)	Å	

b	=	7.1033(11)	Å	 b	=	7.0202(12)	Å	
c	=	11.0940(18)	Å	 c	=	8.8865(16)	Å	
β	=	105.636(3) ° β =	90.015(4)	°	

Volume	 841.9(2) Å3 424.52(13)	Å3	
Z	 4	 2
Density	(calcd.)	 1.232	g/cm3 1.222	g/cm3	
Absorption	coefficient	 0.091	mm‐1 0.091	mm‐1	
F(000)	 336	 168	
Crystal	size/color	 0.35 × 0.15 × 0.08 mm3/colorless 0.35 × 0.15	×	0.05	mm3/colorless
Theta	range	for	data	collection	 3.04	to	27.48	°	 4.76	to	27.42	°	
Index	ranges	 −14	≤	h	≤	14	 −8	≤	h	≤	8	

−9	≤	k	≤	9	 −9	≤	k	≤	8	
−12	≤	l ≤	14 −11	≤	l ≤	11	

Reflections	collected	 8776 4583
Independent	reflections	 1908	[R(int)	=	0.0219] 1028	[R(int)	=	0.0225]	
Completeness	 99.0	% 98.0	%
Absorption	correction	 Multi‐scan	[24] Multi‐scan	[24]	
Max.	and	min.	transmission	 0.9927	and	0.9687 0.9955	and	0.9690	
Refinement	method	 Full‐matrix	least‐squares	on	F2 Full‐matrix	least‐squares	on	F2
Data/restraints/parameters	 1908/0/111	 1028/1/111	
Goodness‐of‐fit	on	F2	 1.041	 1.092	
Final	R	indices	[I	>	2sigma(I)]	 R1	=	0.0437, wR2 =	0.1174 R1 =	0.0299,	wR2	=	0.0789	
R	indices	(all	data)	 R1	=	0.0478,	wR2	=	0.1207	 R1	=	0.0316,	wR2	=	0.0800	
Largest	diff.	peak	and	hole	 0.341	and	−0.191	e	Å−3 0.238 and	−0.117	e	Å−3	
Measurement	 Rigaku/MSC	Mercury	CCD	diffractometer Rigaku/MSC	Mercury	CCD	diffractometer
Program	system	 Crystal Structure [27] Crystal Structure	[27]	
Structure	determination	 Direct	methods	(SIR2008	[25]) Direct	methods	(SIR2008	[25])
CCDC	no	 962338 962341
	

	
The	melting	points	were	measured	using	a	Shimadzu	DSC‐

60	 differential	 scanning	 calorimeter	 (DSC)	 equipment.	 The	
infrared	 (IR)	 spectra	 were	 recorded	 on	 a	 Horiba	 FT‐720	
Fourier	 transform	 infrared	 spectrometer.	 IR	 measurements	
were	carried	out	by	the	KBr	method	at	64	scans	per	spectrum	
with	 4	 cm−1	 resolution.	 1H	 NMR	 spectra	 (500	 MHz)	 and	 13C	
NMR	spectra	(125	MHz)	were	recorded	on	a	JEOL	JNM‐ECA	500	
spectrometer.	

The	X‐ray	diffraction	data	were	collected	at	123(2)	K	by	ω	
scan	 technique	on	 a	Rigaku/MSC	Mercury	CCD	diffractometer	
[23]	equipped	with	graphite‐monochromatized	MoKα	radiation	
(λ	 =	 0.71070	 Å).	 The	 data	 were	 corrected	 for	 Lorentz‐
polarization	and	absorption	effects	[24].	These	structures	were	
solved	 by	 direct	 methods	 using	 SIR2008	 program	 [25]	 and	
refined	 by	 a	 full‐matrix	 least‐squares	 calculation	 on	 F2	 using	
SHELXL‐97	[26].	All	calculations	were	performed	using	Crystal	
Structure	software	package	[27].		

The	 absolute	 configuration	 of	 (S)‐IPrMH	 has	 not	 been	
established	 by	 anomalous	 dispersion	 effects	 in	 diffraction	
measurements	 on	 the	 crystal.	 The	 enantiomer	 has	 been	
assigned	 by	 reference	 to	 an	 unchanging	 chiral	 centre	 in	 the	
synthetic	 procedure	 [28].	 Non‐hydrogen	 atoms	 were	 refined	
anisotropically.	The	hydrogen	atoms	bonded	to	nitrogen	atoms	
were	 located	 in	 a	 difference	 map	 and	 refined	 freely.	 The	
remaining	hydrogen	atoms	were	positioned	geometrically	(C–H	
=	0.98	or	1.00	Å)	and	refined	using	a	riding	model,	with	Uiso(H)	
=	 1.2	 Ueq(C).	 Structures	 were	 visualized	 using	 ORTEP‐3	 for	
windows	[29]	and	Mercury	[30].	Details	on	data	collection	and	
refinement	are	given	in	Table	1.	

	
2.2.	Synthesis	
	

(rac)‐5‐Isopropyl‐5‐methylhydantoin	 was	 synthesized	 by	
slight	modification	of	a	literature	method	[28].	A	1:3	mixture	of	
α‐methyl‐DL‐valine	(0.20	g,	1.53	mmol)	and	urea	(0.27	g,	4.57	
mmol)	were	allowed	to	react	directly	in	the	absence	of	solvent	
at	 150	 °C	 for	 2	 h.	 This	 reaction	 was	 carried	 out	 in	 a	 30	 mL	

round‐bottom	flask	under	stirring	using	an	oil	bath	as	the	heat	
source.	After	the	reaction	was	complete,	water	was	added	while	
the	flask	was	still	warm.	The	solution	was	reheated	to	dissolve	
all	 the	 solids	 and	 allowed	 to	 cool	 to	 room	 temperature,	 then	
placed	in	a	refrigerator	for	3	h.	The	colorless	crystals	removed	
by	 vacuum	 filtration	 were	 further	 purified	 by	 flash	 column	
chromatography	 using	 hexane	 and	 ethyl	 acetate	 as	 eluents.	
Single	 crystals	 suitable	 for	X‐ray	diffraction	were	 obtained	by	
recrystallization	from	an	aqueous	solution.	

(S)‐5‐Isopropyl‐5‐methylhydantoin	 was	 prepared	 through	
the	 reaction	 of	 α‐methyl‐L‐valine	 (0.20	 g,	 1.53	mmol,	 Bachem	
AG,	 Bubendorf,	 Switzerland)	 and	 urea	 (0.27	 g,	 4.57	mmol)	 by	
the	 same	 procedure.	 Single	 crystals	 suitable	 for	 X‐ray	
diffraction	were	obtained	by	recrystallization	from	an	aqueous	
solution.	

(rac)‐5‐Isopropyl‐5‐methylhydantoin	 ((rac)‐IPrMH):	 Color:	
Colorless.	 Yield:	 50%.	M.p.:	 171	 °C.	 FT‐IR	 (KBr,	 ν,	 cm‐1):	 3218	
(NH),	1765	(C=O),	1720	(C=O),	1434	ν(CN)+δ(NH).	1H	NMR	
(500	MHz,	Aceton‐d6,	 δ,	 ppm):	 0.90	 (d,	 3H,	 J	=	6.9	Hz,	 (CH3)2‐
CH),	0.99	(d,	3H,	J	=	6.9	Hz,	(CH3)2‐CH),	1.38	(s,	3H,	CH3‐C),	1.97	
(sep,	1H,	J	=	6.9	Hz,	(CH3)2‐CH),	7.12	(br.	s,	1H,	NH‐CO‐NH‐CO),	
9.58	(br.	s,	1H,	NH‐CO‐NH‐CO).	13C	NMR	(125	MHz,	Aceton‐d6,	δ,	
ppm):	178.81	(1C,	NH‐CO‐NH‐CO),	157.60	(1C,	NH‐CO‐NH‐CO),	
66.53	 (1C,	 CH3‐C),	 34.95	 (1C,	 (CH3)2‐CH),	 22.15	 (1C,	 CH3‐C),	
17.23	(1C,	(CH3)2‐CH),	16.44	(1C,	(CH3)2‐CH).	

(S)‐5‐Isopropyl‐5‐methylhydantoin	 ((S)‐IPrMH):	 Color:	
Colorless.	 Yield:	 60%.	M.p.:	 196	 °C.	 FT‐IR	 (KBr,	 ν,	 cm‐1):	 3218	
(NH),	1765	(C=O),	1720	(C=O),	1434	ν(CN)+δ(NH).	1H	NMR	
(500	MHz,	Aceton‐d6,	 δ,	 ppm):	 0.90	 (d,	 3H,	 J	=	6.9	Hz,	 (CH3)2‐
CH),	0.99	(d,	3H,	J	=	6.9	Hz,	(CH3)2‐CH),	1.37	(s,	3H,	CH3‐C),	1.97	
(sep,	1H,	J	=	6.9	Hz,	(CH3)2‐CH),	7.07	(br.	s,	1H,	NH‐CO‐NH‐CO),	
9.54	(br.	s,	1H,	NH‐CO‐NH‐CO).	13C	NMR	(125	MHz,	Aceton‐d6,	δ,	
ppm):	178.80	(1C,	NH‐CO‐NH‐CO),	157.43	(1C,	NH‐CO‐NH‐CO),	
66.51	 (1C,	 CH3‐C),	 34.97	 (1C,	 (CH3)2‐CH),	 22.19	 (1C,	 CH3‐C),	
17.25	(1C,	(CH3)2‐CH),	16.46	(1C,	(CH3)2‐CH).	
	
	



8	 Ichitani	et	al.	/	European	Journal	of	Chemistry	5	(1)	(2014)	6‐10	
	
3.	Results	and	discussion		
	

(rac)‐IPrMH	 and	 (S)‐IPrMH	 were	 synthesized	 by	 one‐pot	
reaction	 of	 α‐methyl‐DL‐valine	 and	 α‐methyl‐L‐valine	 with	
urea,	 respectively,	 in	 the	 absence	 of	 solvent.	 (S)‐IPrMH	 was	
obtained	 in	 an	 optical	 pure	 form	without	 racemization	 in	 the	
present	reaction	condition.		

Table	 2	 and	 Figure	 2	 summarize	 the	 melting	 points	 and	
solid	 state	 IR	 spectra	 of	 IPrMH.	 (rac)‐IPrMH	 crystal	 shows	 a	
melting	point	of	171	°C,	while	(S)‐IPrMH	melts	at	196	°C.	Thus,	
the	racemic	crystal	of	 IPrMH	has	a	 lower	melting	temperature	
than	the	enantiopure	crystal	by	25	°C.	As	given	in	Figure	2,	the	
IR	 spectrum	 of	 (rac)‐IPrMH	 is	 identical	 with	 that	 of	 the	 pure	
enantiomer.	

	

	
	

Figure	2.	Solid	state	IR	spectra	of	(rac)‐IPrMH	and	(S)‐IPrMH.
	
	

Table	2.	Melting	points	and	solid	state	IR	spectra.	

M.p.	(°C)	
IR	(cm‐1)	
ν(NH)	 ν(C=O)	 ν(CN)+δ(NH)

(rac)‐IPrMH	 171	 3218	 1765,	1720	 1434	
(S)‐IPrMH	 196	 3218	 1765,	1720	 1434	
	

	
When	a	racemate	crystallizes	as	a	conglomerate	(equimolar	

mechanical	 mixtures	 of	 two	 crystalline	 enantiomers),	 the	
melting	point	of	the	conglomerate	is	always	lower	than	that	of	
the	 pure	 enantiomer,	 and	 the	 solid	 state	 IR	 spectra	 of	 the	
conglomerate	 are	 identical	with	 those	of	 the	pure	enantiomer	
[31].	 On	 the	 other	 hand,	 the	 melting	 point	 of	 a	 racemic	
compound	 (equimolar	 enantiomers	 are	 present	 in	 the	 crystal	
lattice)	 is	 generally	 higher	 than	 that	 of	 the	 pure	 enantiomer,	
and	the	solid	state	IR	spectra	of	the	racemic	compound	are	not	
identical	with	those	of	the	pure	enantiomer	[32].		

In	 the	 present	 case,	 the	 melting	 point	 values	 and	 the	 IR	
spectra	 suggest	 the	 conglomerate	 formation	 for	 the	 racemic	
IPrMH	 crystals.	 However,	 the	 single	 crystal	 X‐ray	 diffraction	
data	has	shown	that	the	racemic	IPrMH	doesn’t	crystallize	as	a	
conglomerate	 but	 as	 a	 racemic	 compound.	 Thus,	 this	 study	
presents	 the	 rare	 case	 of	 lower	 melting	 racemic	 and	 higher	
melting	enantiomeric	crystals.	

Table	 1	 shows	 the	 crystallographic	 data.	 Figure	 3	 and	 4	
show	 the	 molecular	 structure	 and	 atom‐labeling	 scheme	 of	
(rac)‐IPrMH	 and	 (S)‐IPrMH,	 respectively.	 Table	 3	 summarizes	
the	 selected	 geometric	 parameters.	 Figure	 5,	 6	 and	7,	 8	 show	
the	crystal	packing	of	(rac)‐IPrMH	and	(S)‐IPrMH,	respectively.	
Table	4	shows	the	hydrogen‐bond	geometry.	As	given	in	Table	
1,	(rac)‐IPrMH	crystallizes	in	the	monoclinic	system	with	space	
group	 P21/n	 and	 four	 molecules	 in	 a	 unit	 cell.	 (S)‐IPrMH	
crystallizes	in	the	monoclinic	system	with	space	group	P21	and	
two	molecules	in	a	unit	cell.	

As	 given	 in	 Figure	 3,	 4	 and	 Table	 3,	 (rac)‐IPrMH	 and	 (S)‐
IPrMH	are	very	similar	in	molecular	geometries.	The	hydantoin	
moieties	 (N1/C1/O1/N2/C2/O2/C3)	 for	 (rac)‐IPrMH	 and	 (S)‐
IPrMH	 are	 nearly	 planar,	 with	 maximum	 deviations	 of	
0.0285(13)	Å	 in	N2	and	0.0467(17)	Å	 in	N2,	respectively.	The	
orientations	of	the	isopropyl	groups,	defined	by	the	C5,	C6	and	

C7	 atoms,	 relative	 to	 these	 planes	 are	 given	 by	 the	 torsion	
angles	 N1−C3−C5−C6	 of	 63.46(14)	 °	 for	 (rac)‐IPrMH	 and	
62.8(2)	°	for	(S)‐IPrMH.	The	N1−C1	distances	[1.3348(14)	Å	for	
(rac)‐IPrMH;	 1.332(2)	 Å	 for	 (S)‐IPrMH]	 are	 shorter	 than	 the	
N2−C1	distances	[1.3818(14)	Å	for	(rac)‐IPrMH;	1.384(2)	Å	for	
(S)‐IPrMH],	and	the	O1−C1−N1	angles	 [127.31(10)	 °	 for	 (rac)‐
IPrMH;	 127.67(17)	 °	 for	 (S)‐IPrMH]	 are	 greater	 than	 the	
O1−C1−N2	angles	[124.35(10)	°	 for	(rac)‐IPrMH;	124.06(17)	°	
for	(S)‐IPrMH].	

	

	
	

Figure	 3.	 Molecular	 structure	 of	 (rac)‐IPrMH.	 Anisotropic	 displacement	
ellipsoids	are	drawn	at	the	50%	probability	level.	
	
	

	
	

Figure	 4.	 Molecular	 structure	 of	 (S)‐IPrMH.	 Anisotropic	 displacement	
ellipsoids	are	drawn	at	the	50%	probability	level.	

	
Table	3.	Selected	geometric	parameters	(Å,	°).	
Geometric	parameters (rac)‐IPrMH	 (S)‐IPrMH
Bond	lengths 	
O1−C1 1.2379(14)	 1.2376(18)
O2−C2 1.2084(15)	 1.202(2)
N1−C1 1.3348(14)	 1.332(2)
N1−C3 1.4652(14)	 1.4638(19)
N2−C1 1.3818(14)	 1.384(2)
N2−C2 1.3751(15)	 1.381(2)
C2−C3	 1.5366(17)	 1.536(2)	
Bond	angles 	
C1−N1−C3 112.83(9)	 113.03(15)
C1−N2−C2 111.55(10)	 111.42(14)
O1−C1−N1 127.31(10)	 127.67(17)
O1−C1−N2	 124.35(10)	 124.06(17)	
N1−C1−N2	 108.34(10)	 108.27(12)	
O2−C2−N2 126.21(11)	 126.08(16)
O2−C2−C3	 127.02(11)	 127.32(15)	
N2−C2−C3	 106.77(9)	 106.60(14)	
N1−C3−C2 100.44(8)	 100.55(13)
Torsion	angles	 	 	
N1−C3−C5−C6	 63.46(14)	 62.8(2)	
N1−C3−C5−C7 −60.23(13)	 −61.22(18)
C2−C3−C5−C6	 −47.44(14)	 −48.4(2)	
C2−C3−C5−C7	 −171.14(10)	 −172.46(14)	
C4−C3−C5−C6 −169.84(12)	 −170.46(19)
C4−C3−C5−C7 66.46(13)	 65.47(19)
	

In	(rac)‐IPrMH	crystal	(Figure	5,	6	and	Table	4),	the	amide	
N1−H	and	N2−H	of	one	molecule	are	hydrogen‐bonded	 to	 the	
amide	O1=C1	groups	of	neighboring	molecules	 to	 form	R22(8)	
[33]	 rings	 [N1···O1i	 2.8334(13)	 Å,	 N1−H···O1i	 168.9(14)	 °;	
N2···O1ii	 2.8226(13)	 Å,	 N2−H···O1ii	 168.9(16)	 °;	 symmetry	
codes:	 (i)	−x+1/2,	y−1/2,	−z+3/2;	 (ii)	−x+1/2,	y+1/2,	−z+3/2].	
The	amide	O2=C2	groups	aren’t	hydrogen‐bonded.	These	rings	
are	 linked	 into	 infinite	 one‐dimensional	 tapes	 around	 a	 two‐



Ichitani	et	al.	/	European	Journal	of	Chemistry	5	(1)	(2014)	6‐10	 9	
 
fold	 screw	axis	 along	 the	b	 axis.	A	 single	 tape	 is	 composed	of	
single	enantiomer	and	itself	is	homochiral.	

	
Table	4.	Hydrogen‐bond	geometry	(Å,	°)	(D‐donor;	A‐acceptor;	H‐hydrogen).	
D−H···A	*	 D−H	 H···A	 D···A	 D−H···A
(rac)‐IPrMH	 	 	 	 	
N1−H···O1i	 0.903(17)	 1.944(15)	 2.8334(13)	 168.9(14)
N2−H···O1ii	 0.862(17)	 1.970(15)	 2.8226(13)	 168.9(16)
(S)‐IPrMH	 	 	 	
N1−H···O1iii	 0.84(3)	 2.02(3)	 2.841(2)	 166(2)
N2−H···O1iv	 0.94(2)	 1.89(2)	 2.819(2)	 169(2)
*	 Symmetry	 codes:	 (i)	 −x+1/2,	 y−1/2,	 −z+3/2;	 (ii)	 −x+1/2,	 y+1/2,	 −z+3/2;	
(iii)	−x,	y+1/2,	−z+2;	(iv)	−x,	y−1/2,	−z+2.	

	

	
	
Figure	5.	Crystal	 packing	of	 (rac)‐IPrMH	viewed	down	 the	a	 axis,	 showing	
the	 hydrogen‐bonded	 one‐dimensional	 (S)‐tape	 running	 along	 the	 b	 axis.	
Hydrogen	bonds	are	shown	as	dashed	cyan	lines	(see	Table	4	for	details).	
	
	

	
	

Figure	6.	Crystal	 packing	of	 (rac)‐IPrMH	viewed	down	 the	b axis,	 showing	
the	stacking	of	(S)‐tapes	and	(R)‐tapes.	

	
As	shown	in	Figure	7	and	Table	4,	(S)‐IPrMH	crystal	is	very	

similar	 to	 (rac)‐IPrMH	 crystal	 in	 N−H···O	 hydrogen‐bonding	
pattern	 [N1···O1iii	 2.841(2)	 Å,	 N1‐H···O1iii	 166(2)	 °;	 N2···O1iv	
2.819(2)	 Å,	 N2−H···O1iv	 169(2)	 °;	 symmetry	 codes:	 (iii)	 −x,	
y+1/2,	 −z+2;	 (iv)	 −x,	 y−1/2,	 −z+2].	 On	 the	 other	 hand,	 (S)‐
IPrMH	crystal	is	quite	different	from	(rac)‐IPrMH	crystal	in	the	
packing	 mode	 of	 the	 one‐dimentional	 tapes	 by	 the	 hydrogen	
bonds.	As	shown	in	Figure	6,	(rac)‐IPrMH	crystal	 is	formed	by	
the	 alternate	 packing	 of	 two	 different	 kinds	 of	 homochiral	
tapes,	represented	as	(S)‐tapes	and	(R)‐tapes.	(S)‐IPrMH	crystal	
is	formed	by	the	packing	of	only	(S)‐tapes	(Figure	8).		
	
4.	Conclusion	
	

The	 racemic	 IPrMH	 exhibits	 lower	 melting	 temperature	
than	the	pure	enantiomer	by	25	°C.	The	solid	state	IR	spectrum	
of	 the	 racemic	 IPrMH	 is	 identical	 with	 that	 of	 the	 pure	
enantiomer.	These	experimental	 results	suggest	the	 formation	
of	 conglomerate	 crystals.	 Nevertheless,	 the	 racemic	 IPrMH	
doesn’t	 crystallize	 as	 a	 conglomerate	 but	 as	 a	 racemic	

compound.	 In	 the	 racemic	 and	 the	 enantiomeric	 crystals,	 the	
molecular	 geometries	 and	 the	 intermolecular	 interactions	 are	
very	similar	 to	 each	other.	 In	 the	both	cases,	 the	 amide	N1−H	
and	N2−H	of	one	molecule	are	hydrogen‐bonded	to	the	amide	
O1=C1	 groups	 of	 neighboring	molecules	 to	 form	R22(8)	 rings,	
and	 these	rings	are	 linked	 into	 infinite	one‐dimensional	 tapes.	
In	 the	 racemic	 crystal,	 a	 single	 tape	 is	 composed	 of	 single	
enantiomer	and	itself	is	homochiral.	
	

	
	

Figure	7.	Crystal	packing	of	(S)‐IPrMH	viewed	down	the	a	axis,	showing	the	
hydrogen‐bonded	one‐dimensional	 tape	running	along	the	b	axis.	Hydrogen	
bonds	are	shown	as	dashed	cyan	lines	(see	Table	4	for	details).	
	
	

	
	

Figure	8.	Crystal	packing	of	(S)‐IPrMH	viewed	down	the	b	axis,	showing	the	
stacking	of	(S)‐tapes.	
	
Supplementary	materials	
	

CCDC‐962338	 and	 CCDC‐962341	 contain	 the	
supplementary	crystallographic	data	for	this	paper.	These	data	
can	 be	 obtained	 free	 of	 charge	 via	
www.ccdc.cam.ac.uk/data_request/cif,	 or	 by	 e‐mailing	
data_request@ccdc.cam.ac.uk	,	or	by	contacting	The	Cambridge	
Crystallographic	 Data	 Centre,	 12	 Union	 Road,	 Cambridge	 CB2	
1EZ,	UK;	fax:	+44(0)1223‐336033.	
	
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