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The Ultimate NMR Software for Structure Characterization

1. We
first
need
analyze
what
the
information
the
mass
spectroscopy
is
telling
us.

The
first
 m/z
value
is
the
M
peak,
which
tells
us
how
many
nitrogen
atoms
are
present
in
the
 molecular
formula.

If
the
m/z
value
is
even,
then
there
are
zero
or
an
even
amount
of
 nitrogen
atoms.

If
the
m/z
value
is
odd,
then
there
are
an
odd
amount
of
nitrogen
atoms. In
this
example,
the
M
peak
has
an
intensity
of
154.

This
is
an
even
number,
so
there
 are
0
or
an
even
amount
of
nitrogens
in
the
structure. The
second
value
is
the
M+1
peak,
which
tells
us
how
many
carbons
are
present
in
the
 structure.

How
you
find
this
is
by
dividing
the
relative
abundance
of
the
M+1
peak
by
1.1%.

 MAKE
SURE
YOU
DO
NOT
DIVIDE
BY
1%;
THIS
WILL
NOT
GIVE
YOU
THE
RIGHT
ANSWER.

 In
this
example,
the
M+1
peak
relative
abundance
is
11.23%.

You
divide
this
by
1.1%
 and
you
get
10.209%.

This
means
that
the
structure
has
either
10
or
11
carbons. The
third
value
is
the
M+2
peak,
which
tells
us
how
many
(if
any)
bromine,
chlorine,
or
 sulfur
atoms
are
present
within
the
structure.

If
the
relative
abundance
is
approximately
 4%,
then sulfur
is
present.

If
the
relative
abundance
is
approximately
33%,
then chlorine
is
 present.

If
the
relative
abundance
is
approximately
100%,
then
bromine is present. In
this
example,
the
M+2
peak
relative
abundance
is
0.26%.

This
does
not
correspond
to
 any
of
the
above
stated
elements,
and
is
too
small
to
be
sulfur,
so
there
is
no
chlorine,
 bromine
or
sulfur
atoms
present
in
this
molecule. We
can
now
use
this
information
to
find
a
molecular
formula
for
this
structure. C10
Possibility 154
–
(12 amu
per
C
x
10C)
=
34
amu
left
for
hydrogen,
nitrogen
and
oxygen In
this
case,
we
can
rule
out
C10H6N2 because
the
IR
spectrum
shows
that
there
is
a
carbonyl
 in
Zone
4,
thus
revealing
an
oxygen
in
the
formula.

C10H6N2 lacks
an
oxygen.

You
can
also
 rule
out
C10H202
because
it
does
not
correspond
with
the
integrals
given
in
the
1 H‐NMR.

 The
integral
equals
9
(2+1+6),
and
H2 is
not
a
proportionate
ratio.

That
leaves
us
with
 C10H180
as
our
formula.