Close Amide NH···F Hydrogen Bonding Interactions in 1,8-Disubstituted Naphthalenes

Article abstract of DOI:10.1021/acs.joc.0c00553

In this note, we present a series of N-(8-fluoronaphthalen-1-yl)benzamide derivatives designed to maximize amide-NH···F hydrogen bond interactions therein. A combination of IR and NMR spectroscopy indicates a linear correlation between the high energy shi

Full text of DOI:10.1021/acs.joc.0c00553

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Note
Close Amide NH···F Hydrogen Bonding
Interactions in 1,8-Disubstituted Naphthalenes
Muhammad Kazim, Maxime A. Siegler, and Thomas Lectka
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.0c00553 • Publication Date (Web): 31 Mar 2020
Downloaded from pubs.acs.org on April 4, 2020
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Close Amide NH···F Hydrogen Bonding Interactions in 1,8-
Disubstituted Naphthalenes
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Muhammad Kazim, Maxime A. Siegler and Thomas Lectka*
Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218.
would once again serve as excellent models for the study of amide-
NH···F interactions (Figure 1).
ABSTRACT:
In this note, we present a series of N-(8-
fluoronaphthalen-1-yl)benzamide derivatives designed to maximize
amide-NH···F hydrogen bond interactions therein. A combination of
IR and NMR spectroscopy indicates a linear correlation between the
high energy shift in NH stretching frequency and the electron
withdrawing nature of the substituent, consistent with the trend
predicted by DFT calculations. Additionally, a limiting case of
hydrogen bonding is observed when the benzamide derivatives are
replaced with trifluoroacetamide, causing an additional red shift of 44
cm-1 in the NH stretching frequency. Most importantly, 1H-19F
coupling constants in this series are among the largest measured for
amide-NH···F interactions. X-ray crystallography reveals face-to-face
alignment of naphthalene rings in these derivatives resulting in part
from the NH···F hydrogen bonds. This motif also dictates the
formation of sheets composed of stacked naphthalene rings in the
crystal structure as opposed to unfluorinated analogues wherein
NH···OC hydrogen-bonding interactions force benzamide and
naphthalene rings to engage in T-shaped  interactions instead.
Additionally, the NH proton in the trifluoroacetamide derivative
engages in extended H-bond interactions in its crystal structure.
R
effects of varying R on
NH---F interaction
H
F
N
O
Figure 1. The NH···F Interaction in N-(8-fluoronaphthalen-1-
yl)benzamide derivatives
Chemical intuition suggests that the trans-amide conformation of
these N-(8-fluoronaphthalen-1-yl)benzamide derivatives would make
the N-H proton particularly available to engage in hydrogen
bonding to the neighboring “peri” fluorine atom. On the other hand,
 interactions in aromatic compounds21-24 are well known to
skew the rotameric preferences of aryl amides. To shed light on
the relative stabilities of the rotamers - and thereby possible H-
bonding interactions - we turned to DFT calculations. At
B97XD/6-311+G**, we located the cis and trans rotamers for
each derivative (Figure 2, see supporting information “SI” for
details). In trans structures 1-4, the NH hydrogen resides at a
position maximizing the NH···F interaction, whereas it bends out
of the plane of naphthalene ring in cis structures 1a-4a, thus
attenuating the interaction (Figure 2). As it were, the desired
rotamers were predicted to be more stable by at least 2.3 kcal/mol
as we would ordinarily expect. Additionally, the amide NH···F
distances in the series 1-4 are predicted to lie in the range of 1.84-
1.86 Å (gas phase), smaller than the shortest distance of 1.93 Å
observed crystallographically.14
The interaction of C-F bonds, especially in proteins, with
proximate functional groups is a topic of lively interest and
discussion.1-6 Their importance in dictating protein structure and
function is not yet fully answered, including the dilemma of
whether such interactions themselves are due to propinquity,
attractive interactions, or a combination thereof. Over the past
several years we have investigated close interactions between C-F
bonds and common organic functional groups in relatively small
molecules that are often dictated by forced proximity, along with
some measure of attraction and repulsion.7-13 The case of the amide
NH···F interaction is presumably one of the more interesting, due
to the ubiquity of amide residues in proteins. Nevertheless, a search
of the Cambridge Crystallographic Database (CCD) indicates only
a few substantial interactions; most are self-evidently weak and
R
long range.
The closest such interaction we found was
O
approximately 1.93 Å.14 We thought it would be illustrative and
useful to investigate the closest range and thus strongest model
interaction we could conceive in order to achieve a fuller
understanding. In this note, we employ the 1,8-disubstituted
naphthalene scaffold to investigate a series of amide NH···F
interactions that are by spectroscopic measures more intense than
those exhibited in the available crystal structure database.
Historically, these so-called "proton sponge" derivatives have often
been used to investigate the nature of close H-bonding
interactions.15-20 We imagined that a series of these molecules
H
H
F
N
O
F
N
R
1-4
1a-4a
disfavored
favored
Figure 2. Rotameric forms located by DFT calculations (B97XD/6-
311+G**) with 1-4 favored over 1a-4a by >2.7 kcal/mol.
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N
Curiously, replacing the fluorine with hydrogen attenuates the
NH2 NH2
N
NH
1
2
3
4
5
6
7
8
preference for the desired rotamer and no stability trend is observed
when test molecules 5 were optimized at the same level of theory
(Figure 3, Table S2). In fact, the NH proton bends out of the plane
of the naphthalene ring in both optimized rotamers (See SI).
Similarly, no noticeable trend was observed when rotamers of 7-
fluoro-1-aminonaphthalene derivatives were optimized (6, Figure
3, Table S3). These calculations suggested to us that the relative
stability of desired rotamers could be attributed in part to favorable
NH···F interactions. Therefore, having a fluorine atom at that
position may prove essential to the investigation as it locks the
structure in the desired orientation.
(CH3)2CH(CH2)2ONO2
HF, pyridine
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8
R
O
Cl
F
NH2
R
H
9
F
N
O
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Et3N
1. R = OMe
2. R = H
3. R = NO2
10
R
NMe2
NO2
O
H
H
N
O
H
N
H
F
N
O
F
N
O
X
X
1. H2, Pd/C
2. MeI, K2CO3
R
5: X = H
6: X = F
K = from > 1 to < 1
3
4
Scheme 1. Synthesis of N-(8-fluoronahphthalen-1-yl) benzamide
derivatives.
Figure 3. Rotamers of 5 and 6 optimized for rotameric preferences with
DFT calculations at B97XD/6-311+G**; R = NMe2; OMe; H; NO2.
The two rotamers can easily be distinguished based on the NH···F
spin-spin coupling constants predicted by DFT calculations
After DFT calculations pointed us in the right direction, we
synthesized the desired molecules from commercially available
1,8-diaminonaphthalene 8. Treatment of 8 with isoamyl nitrite
followed by HF-pyridine resulted in the formation of 8-fluoro-1-
aminonaphthalene 10,25 which was then acetylated with a series of
substituted benzoyl chlorides to afford N-(8-fluoronahphthalen-1-
yl)benzamide derivatives in 75-85% yields (Scheme 1). The
dimethylamino analogue 4 was synthesized by reduction/alkylation
of p-NO2 derivative 3 (Scheme 1).
(B3LYP/6-311++G**).
In trans-amide conformations, the
calculated coupling constants lie between 24-27 Hz, whereas for
the undesired rotamers as well as rotamers of 5 and 6 those numbers
drop to 0-2 Hz. Experimentally, the 1H NMR spectra of all
derivatives show NH protons as apparent doublets (JH-F = 20-21 Hz).
On the other hand, the 19F NMR spectra reveal complex multiplets
(See SI). Both 1H and 19F NMR spectra indicate that the products
of Scheme 1 are locked exclusively in the desired trans orientation.
The 19F NMR of all the derivatives also reveal consistent 16 Hz
coupling constants corresponding to the interaction of the F nucleus
with the ortho proton on the naphthalene ring system16 (calcd 16.4
Hz, Figure 4). Additionally, the coupling constants for the series
are predicted to show a slight increase as the substituent on the
benzene ring becomes more electron withdrawing (from 24.7 Hz
for p-NMe2 to 27 Hz for p-NO2). However, this modest trend is
not clearly discernable in the actual 19F NMR data primarily due to
the complex nature of the multiplets.
NO2
calcd: 27 Hz; obs 21 Hz
calcd: 16.4 Hz; obs: 16 Hz
H
F
N
O
H
Figure 4. Major coupling constants observed experimentally and
predicted by B3LYP/6-311++G** (compound 3).
We then conducted an IR analysis of the NH···F interactions. It
is generally accepted that the increasing strength of a classical
hydrogen bond results in lengthening of the donor-H bond and an
attendant shortening of the acceptor-H distance, inducing a red shift
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in the IR-stretching frequency.26-30 An initial DFT analysis
1
2
3
4
(B97XD/6-311+G**) of the synthesized molecules predicts a
similar trend for NH stretches in the IR as the nature of substituent
becomes more electron withdrawing, a possible indication of
increasing hydrogen bond strength (Table 1).
5
6
Table 1. Calculated (scaled) and experimentally observed NH
stretching frequencies in 1 through 4.
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Figure 6. X-ray crystal structure of p-NO2 benzamide derivative (3)
with extended hydrogen bonding network forming sheets of
naphthalene rings.
The NH stretch in the experimentally observed IR spectra of the
derivatives shows a continuous high energy shift as the aromatic
ring becomes more electron deficient. The NH stretch of p-NO2
derivative appears at 3470.5 cm-1, which is ca. 16 cm-1 red shifted
compared to the same stretch in the p-NMe2 derivative, thus
implying a significantly stronger H bond in the former case (Table
1 and Figure 5). Although substituent effects have a relatively
smaller effect on high energy shifts in the NH stretching frequency
of benzamides, this fact does not necessarily imply a weak
substituent effect on the hydrogen bond strength itself since the
high energy shift in IR is considered only a semi-quantitative
measure.31
Finally, we imagined that an even larger high energy IR shift
could be observed if the substituent is more electron withdrawing
than p-NO2Ph. A DFT analysis predicted that replacing the
benzamide derivatives with trifluoroacetamide would show a
significant red shift of an additional 39 cm-1 in NH stretching
frequency compared to p-NO2Ph derivative. In fact, when 8-
fluoro-1-aminonaphthalene is acetylated with trifluoroacetic
anhydride (Scheme 2, 86%), the NH stretch of the product appears
at 3443 cm-1, red shifted by 28 cm-1 compared to the p-NO2
derivative (Figure 7). Additionally, its 19F NMR spectrum shows a
multiplet corresponding to aromatic fluorine with a spin-spin
coupling constant of 19.1 Hz to the proximate N-H, even larger
than that observed in 3.
0.0015
NMe2
O
0.001
OMe
O
O
H
F
NH2
F
N
CF3
0.0005
F3C
O
CF3
Et3N
0
H
11
10
-0.0005
NO2
Scheme 2. Synthesis of the trifluoroacetamide derivative 11.
-0.001
-0.8
-0.2
0.2
0.8

Figure 5: Experimentally observed NH stretches in IR spectra; red (p-
NMe2); purple (p-OMe); blue (p-H); green (p-NO2).
X-ray crystallographic analysis gives additional insight into the
influence of fluorine substitution on crystal packing. We recently
reported the crystal structure of a substituted trityl fluoride that is
significantly different than the corresponding trityl hydride,
confirming the inability of fluorine to act as an “isostere” for
hydrogen when it comes to directionality/ordering.32 Single crystal
X-ray analysis of the p-NO2 derivative 3 reveals an interesting
feature; the naphthalene rings are aligned face to face in a 
interaction (Figure 6), which is significantly different than the
crystal structure of N-(naphthalen-1-yl)benzamide, wherein the
phenyl ring engages in T-shaped  interactions with the
naphthalene ring system.33 This motif results in the formation of
naphthalene-based sheets held by intermolecular hydrogen bonding
between the amide N-H and a neighboring molecule’s carbonyl
oxygen at 2.12 Å. Moreover, the NH···F and N-H distances of 2.22
Å and 0.87 Å are observed in the crystal structure of p-NO2
benzamide derivative (Figure 6, See SI for details).
Figure 7. Experimentally observed NH stretches in IR spectra; red (p-
NO2Ph) peak at 3470.5 cm-1; blue (CF3) peak at 3442.9 cm-1.
Single crystal X-ray analysis of the trifluoroacetamide derivative
11 also reveals an interesting structure. Similar to the benzamide
derivatives, the crystal is characterized by sheets and bifurcated C-
F···HN bonding with an amide carbonyl oxygen and fluorine on
position 8 of the naphthalene ring (NH···F, 2.12 Å), (NH···O, 2.19
Å), (N-H···F3C, 2.25 Å).
Another interesting feature of
trifluorobenzamide derivative’s crystal structure is the close F···F
distance (2.98 Å) between the neighboring molecules’ CF3 groups
(Figure 8).
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Figure 9: Correlation between calculated NH···F distances and
corresponding coupling constants calculated at B3LYP/6-311++G**
using molecules 1-4 and 11-20. See SI for details.
1
2
3
4
Conclusion
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6
7
8
In this note, we have synthesized
fluoronaphthalen-1-yl)benzamide derivatives and established a
correlation between the strength of NH···F hydrogen bonding
interaction and substituents on the benzamide ring. Both H and
a series of N-(8-
1
19F NMR spectra indicate the exclusive formation of the desired
geometry, attributed to the favorable hydrogen bonding
interactions, most notably through strong spin-spin coupling of H
and F. Moreover, IR analysis of the series predicts a direct
correlation between the electron withdrawing nature of substituent
and the hydrogen bond strength. X-ray crystallographic analysis
reveals the formation of sheets characterized by face-to-face 
interactions between the naphthalene rings. We hope that these
results provide additional insights into the increasingly important
role of fluorine in hydrogen bonding interactions.
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Figure 8. X-ray crystal structure of trifluoroacetamide derivative 11
depicting an extended hydrogen bonding network forming sheets of
naphthalene rings.
The X-ray crystal structures of 3 and 11, however, depict amide
NH···F distances of 2.22 Å and 2.12 Å respectively, which are
greater than the shortest NH···F distance found in the CCD and our
predicted gas phase distances. This increased distance in the crystal
structures can be attributed to intermolecular hydrogen bonding
with neighboring molecule’s carbonyl oxygen. In dilute solutions,
however, we conclude that the intramolecular NH···F interaction
dominates and the distance could be approximated to, or even
smaller, than 1.93 Å. We optimized a few of the structures with the
shortest NH···F distances reported in the CCD34-37 at B97XD/6-
311+G** and calculated spin-spin coupling constants for the
NH···F interactions therein at B3LYP/6-311++G** (See SI for
structures and computational details). DFT calculations predict an
inverse correlation of the NH···F coupling constants and distances
between the interacting nuclei (Figure 9). The largest amide
NH···F coupling constant reported in the literature is 17.1 Hz.35
This is smaller than those observed in our molecules which are,
both predicted and experimentally, more than 20 Hz, indicating the
possibility of an amide NH···F distance shorter than those observed
so far. The trend in Figure 9 predicts NH···F distances in the series
of our benzamide derivatives to be approximately 1.90 Å in dilute
solutions, in line with DFT geometry calculations. However, when
it comes to crystal packing, the NH proton skews out of the plane
of naphthalene ring as a result of competitive intermolecular
NH···OC hydrogen bonding.
Experimental Section
1H and 13C spectra were acquired on a 400 MHz NMR in CDCl3
at 25 °C while 19F spectra were acquired on a 300 MHz NMR in
CDCl3. The 1H, 13C and 19F chemical shifts are given in parts per
million (δ) with respect to an internal tetramethylsilane (TMS, δ
0.00 ppm) standard. NMR data are reported in the following
format: chemical shifts (multiplicity (s = singlet, d = doublet, t =
triplet, q = quartet m = multiplet), coupling constants [Hz],
integration). IR data were obtained using an FT-IR with a flat CaF2
cell. HRMS data were obtained on a Thermo Scientific Q-Exactive
Orbitrap mass spectrometer.
General protocol for synthesis of the N-(8-
fluoronaphthalen-1-yl)benzamide derivatives: To
a
solution of 10 in 10 mL CH2Cl2, 1 equiv. of the appropriate benzoyl
chloride derivative was added at room temperature. To the
mixture, 0.1 mL Et3N was added and the solution was stirred at
room temperature for 2 h. The solvent was evaporated under
reduced pressure and the desired product was purified with MPLC
using hexanes and ethyl acetate as eluents.
N-(8-fluoronaphthalen-1-yl)-4-methoxybenzamide (compound 1).
Compound 1 was synthesized following the general protocol for
benzamide derivative synthesis and isolated as colorless crystalline
solid (135 mg, 75% isolated yield). 1H NMR (CDCl3)  9.6 (d, J =
20.6 Hz, 1H), 8.76 (d, J = 7.7 Hz, 1H), 7.94 (d, J = 8.7 Hz, 1H),
7.5–7.66 (m, 3H), 7.3–7.4 (m, 1H), 7.1–7.2 (m, 1H), 7.01 (d, J =
8.7Hz, 1H), 3.88 (s, 3H); 13C NMR {1H} (CDCl3)  165, 164.97,
165.5, 160.3, 157.9, 136.6, 136.5, 132.93, 132.89, 128.8, 127.4,
127.30, 127.29, 125.56, 125.46, 125.41, 125.38, 123.70, 123.67,
118.32, 118.30, 115.05, 114.97, 114.1, 111.3, 111.1, 55.5; 19F
NMR (CDCl3)   m, 1F); 19F NMR {1H} (CDCl3)   s,
1F); IR 3482, 1675, 1606, 1537, 1495, 1432, 1341 (cm-1, CaF2,
CH2Cl2); FTMS (ESI) m/z: [M + H]+ Calcd for C18H15FNO2+
296.1081; Found 296.1076.
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N-(8-fluoronaphthalen-1-yl)benzamide (compound 2). Compound
2 was synthesized following the general protocol for benzamide
derivative synthesis and isolated as a light pink solid (145 mg, 80%
isolated yield). 1H NMR (CDCl3)  9.69 (d, J = 20.8 Hz, 1H), 8.73
(d, J = 7.86 Hz, 1H), 8.38 (m, 2H), 8.13 (m, 2H), 7.7 (m, 2H), 7.5–
7.6 (t, J = 8 Hz, 1H), 7.4–7.47 (m, 1H), 7.19–7.25 (m, 1H); 13C
NMR {1H} (CDCl3)  163.3, 160.1, 157.7, 149.8, 140.7, 136.51,
1.8
1.9
2
2.1
NH---F distance (Å)
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136.48, 131.95, 131.91, 128.1, 127.23, 127.21, 125.93, 125.82,
ASSOCIATED CONTENT
Supporting Information
NMR spectra, crystal structure data, and computational information
are included in the Supporting Information.
1
2
3
4
125.62, 125.59, 124.81, 124.79, 124.2, 118.91, 118.89, 150.07,
149.99, 111.7, 111.5; 19F NMR (CDCl3)   m, 1F); 19F
NMR {1H} (CDCl3)   s, 1F); IR 3477, 1681, 1541, 1487,
1432, 1342 (cm-1, CaF2, CH2Cl2); FTMS (ESI) m/z: [M + H]+
Calcd for C17H13FNO+ 266.0976; Found 266.0970.
5
6
7
8
Crystal Structure of Compound 3 (CCDC 1987532)
Crystal Structure of Compound 11 (CCDC 1987533)
N-(8-fluoronaphthalen-1-yl)-4-nitrobenzamide (compound 3).
Compound 3 was synthesized following the general protocol for
benzamide derivative synthesis and isolated as a yellow solid (162
mg, 85% isolated yield). 1H NMR (CDCl3)  9.7 (d, J = 21 Hz, 1H),
8.79 (m, 1H), 7.98 (m, 1H), 7.5–7.68 (m, 6H), 7.34–7.42 (m, 1H),
7.15–7.23 (m, 1H); 13C NMR {1H} (CDCl3)  165.45, 165.43,
160.3, 157.8, 136.55, 136.51, 135.2, 132.72, 132.68, 131.9, 128.9,
127.30, 127.29, 126.9, 125.6, 125.5, 125.44, 125.40, 123.98,
123.95, 118.49, 118.47, 115.1, 115, 111.4, 111.2; 19F NMR
(CDCl3)   m, 1F); 19F NMR {1H} (CDCl3)   s, 1F);
IR 3470, 1688, 1606, 1540, 1531, 1503, 1487, 1347 (cm-1, CaF2,
CH2Cl2); FTMS (ESI) m/z: [M + H]+ Calcd for C17H12FN2O3+
311.0826; Found 311.0819.
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AUTHOR INFORMATION
Corresponding Author
* Email: lectka@jhu.edu
ORCID
Muhammad Kazim: 0000-0003-2020-8952
Notes
Synthesis of 4-(dimethylamino)-N-(8-fluoronaphthalen-
1-yl)benzamide (compound 4): Compound 3 (100 mg, 0.32
mmol) was dissolved in 30 mL EtOH:THF (2:1) and Pd/C was
added to the solution. The mixture was purged with H2 gas until
TLC indicated complete consumption of 3 and the mixture was
purged with excess H2 gas for another 30 min. Pd/C was then
filtered through celite and the cake was washed with 15 mL THF.
The authors declare no competing financial interest.
ACKNOWLEDGMENT
T.L. thanks the National Science Foundation (Grant CHE 1800510)
for financial support. Mass spectral data were obtained at
University of Delaware’s mass spectrometry center.
1
The solvent was evaporated under reduced pressure and the H
NMR of mixture indicated complete conversion of NO2 to NH2.
The intermediate p-NH2 derivative was utilized without further
purification. It was dissolved in 20 mL EtOH, 200 mg (1.45 mmol)
of K2CO3 and 0.1 mL (1.6 mmol) MeI were added to the mixture
and the solution was refluxed overnight. The reaction mixture was
filtered over Celite, washed with 10 mL EtOH and filtrate was
evaporated under reduced pressure. The dimethylated product was
isolated by MPLC using hexanes and ethyl acetate as eluent as a
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in
the
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light pink solid (35 mg, 35% isolated yield). H NMR (CDCl3) 
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Kawahara, S.; Tsuzuki, S.; Uchimaru, T. Theoretical Study
of the C-F/ Interaction: Attractive Interaction Between
Fluorinated Alkane and an Electron-Deficient -System. J.
Phys. Chem. A 2004, 108, 6744-6749.
9.63 (d, J = 21.1 Hz, 1H), 8.82 (m, 1H), 7.88 (m, 2H), 7.5–7.67 (m,
3H), 7.3–7.41 (m, 1H), 7.12–7.22 (m, 1H), 6.76 (m, 2H), 3.06 (s,
6H); 13C NMR {1H} (CDCl3)  165.49, 165.47, 160.5, 158.1,
152.7, 136.62, 136.58, 128.5, 127.42, 127.40, 125.42, 125.38,
125.35, 125.32, 123.17, 123.14, 121.8, 117.97, 117.95, 114.98,
114.90, 111.3, 111.2, 110.9, 40.1; 19F NMR (CDCl3)   m,
1F); 19F NMR {1H} (CDCl3)   s, 1F); IR 3486, 1669,
1607, 1541, 1526, 1501 (cm-1, CaF2, CH2Cl2); FTMS (ESI) m/z:
[M + H]+ Calcd for C19H18FN2O+ 309.1398; Found 309.1392.
2
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Synthesis of 2,2,2-trifluoro-N-(8-fluoronaphthalen-1-
yl)acetamide (compound 11): To a solution of 10 (110 mg,
0.68 mmol) in 10 mL DCM was added 0.1 mL (0.7 mmol) of
trifluoroacetic anhydride and 0.1 mL Et3N. After stirring at room
temperature for 2 h, the solvent was evaporated under reduced
pressure and the product was purified on MPLC using hexanes and
ethyl acetate as eluents as a white solid (150 mg, 86% isolated
yield). 1H NMR (CDCl3)  9.7 (d, J = 19.9 Hz, 1H), 8.52 (m, 1H),
7.6–7.8 (m, 2H), 7.5–7.59 (m, 1H), 7.4–7.49 (m, 1H), 7.15–7.3 (m,
1H); 13C NMR {1H} (CDCl3)  159.7, 157.3, 155, 154.6, 136.31,
136.28, 129.74, 129.70, 126.96, 126.94, 126.3, 126.2, 125.97,
125.94, 125.50, 125.46, 120.1, 119.36, 119.34, 117.3, 115.0, 114.9,
114.4, 112.1, 111.9; 19F NMR (CDCl3)   m, 1F), 76.19
(s, 3F); IR 3443, 1737, 1638, 1555, 1507, 1443, 1382 (cm-1, CaF2,
CH2Cl2); FTMS (ESI) m/z: [M + H]+ Calcd for C12H8F4NO+
258.0536; Found 258.0530.
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