[CHEM 2320] - Midterm Exam Guide - Everything you need to know! (60 pages long)

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CHEM 2320
MIDTERM EXAM
STUDY GUIDE
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chapter 13
Mass spectrometry ,Infrared Spectrometry ,and Wthavioletl Visible spectroscopy
Useful to Know The Structure of a compound .
Can't synthesize compound without knowing its Structure ..
e In the past ,many inefficient procedures were used to characterize compounds .
These procedures required higher amounts of sample .
More accurate and efficient methods :
.Mass Spectrometry -molecular mass *no electromagnetic radiation
-molecular tormwla spectrometry Us .spectroscopy
-Structural features .Spectroscopy is atechnique that involves the
,through bond vibrations interaction of molecules with electromagnetic
in equal energies as light .
Infrared Spectroscopy -functional groups .radiation .
aUltraviolet CUV )1visible spectroscopy
-comugated double bonds
.(
t.su Stems )
.Nuclear Magnetic Spectroscopy -Uses radio waves to detect nuclear spins .
Mass Spectroscopy -Detects H-Cand provides into about The number and type
Use very small sample .
of advent Atoms /environment .
sample spectrometers vaporized ionized
(electron is removed
from each molecule )
Electron ionization CEA
Beam of high energy
electrons
electron beam MI
M-
radical cation Electron
aElectron bombardment introduces alot of kinetic energy into The molecular ions That most of
break apart into smaller Cations ,radicals ,neutral molecules ,and other radical cations .
eWeakest bonds break easily And result in the formation of most stable products ,
Miz is The molecular mass of The fragment because each fragment has charge +1 .
Only positively charged species reach The collector .
,
Degree of carved path depends on M:Z ratio .
Fragment with smaller m: z ratio will
bend more than that of heavier
-
'magnets deflect
positively charged fragments
fragment .
)positively
in acurved path .
charred It fragment 's Path matches the aerva -
fragments
go between twte Of the analyzer Tube ,The trag -
these plates .
neutral fragments Merit will pass Through the take and
are not accelerated .
out the icon exit slit .
Mass spectrometer records amass spectrum .
.Graph of relative abundance of each More stable fragments arrive unchan -
fragment against ME value .ged at The collector .
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Fragmentation
.Each compound has aunique mass spectrum .Like afingerprint .
Nominal molecular Mass -molecular mass to The nearest whole number of one of The fragments .
Example
Pentane has molecular mass of 72.0939
nominal molecular mass of 72 .
The peak With the highest M:z value is 72 .
molecular ion (M)
fragment that results when an e-
is Knocked out of The molecule .
Thus ,The molecular mass of the compound is given by the miz value of The M.
°Which bond loses The electron is unknown .
electron beam
CHZCHZCHZCHZCHZ -[CH3 CHZCHZCHZ
CH3]± + e
-
molecular ion
M:-2=72
Peaks with smaller m:Zvalues Are called fragment on peaks .
positively charged fragments of M.
Base peak is The tallest peak ;has The greatest relative abundance .
.Assigned relative abundance of loot .,and relative abundance of The other peaks is a
percentage of It .
Amass spectrum gives Us information about the compound because The M:z values and
and relative abundances of The fragments depend on the strength of the molecular ion 's bonds
and The Stability ot the fragments .
weak bonds break in preference to strong bonds ,
and bonds that break to form more Stable
fragments break in preference to Those that form less Stable fragments .
Even though C- Cbonds In Pentane are equal in strength ,the C2- Czbond is more likely to
bleak because It yields The most Stable cation .
Primary Carbo cation
Primary radical }most stable
CZCZ ion fragmentation have M:-2 of 43 and 29 .
a-(2M:Z57 And 15 .
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