Chapter 12 Flashcards
Spectroscopy: technique used to determine the ______ of a compound, most techniques are _______
structure
nondestructive
The _______ (v) of a wave is the number of complete wave cycles that pass a fixed point in a second
frequency
_______ (λ) is the distance between any 2 peaks of the wave
wavelength
frequency and wavelength are _______ proportional
inversely
Low E has _______ v and _______ λ
low
long
High E has _______ v and _______ λ
high
short
Infrared spectroscopy (___): used to determine _______ present in a molecule
IR
functional groups
Bond stretching frequencies:
1) frequency _______ with increasing atomic mass
2) frequency _______ with increasing bond energy (strength)
1) decreases
2) increases
Which has higher frequency on IR, stretching or bending
stretching
1) Stronger bonds absorb at _______ wavenumbers
2) Bonds to smaller mass absorb at _______ wavenumbers
higher
higher
IR-active: vibrations must change the overall _______ of the molecule
dipole moment
Each molecule has a _______ resulting spectrum of IR
unique
Where is the magic line in IR?
3000 cm-1
Conjugations _______ the frequency
weaker bonds
lower
IR in hydrocarbons experience C-C _______
stretch
IR in hydrocarbons experience C-H _______
stretch
A greater percent of S character in the hybrid orbitals will make the C-H bond _______ leading to _______ wavenumber
stronger
Higher
When an alkene has approx frequencies at 990, and 910 cm-1 then you can assume its _______
monosubstituted
Because alcohol (O-H) bond can participate in hydrogen bonding, the IR appearance is _______ and centers around _______
broad
3350
Because carboxylic acid (CO2H) bond can participate in a lot of hydrogen bonding, the IR appearance is _______ and centers around _______
ultra broad
3000
1° RNH2 has _______ appearance on IR
2 weak bends
2° R2NH has _______ appearance on IR
1 weak bend
3° R3N has _______ appearance on IR
NA
Conjugation in carbonyl compounds _______ the position of IR by _____-_____ cm-1
lowers
20-40
If C of the C=O is in a 5 membered ring or smaller, IR shifts to _______ position by _____ cm-1
higher
~30
MS measures _______, which can then be used to determine molecular formula
molecular weight
In MS, a beam of high-energy electrons breaks the molecule apart by “_______” an electron out of it
knocking
MS is a _______ technique: the sample cannot be recovered
destructive
Fragmentation gives a mixture of two fragments, a _______ and a _______
cation and radical
MS only detects the _______ charged fragments!
positively
What are the two important terminology in MS?
1) parent ion [M+]
2) base peak
Parent ion [M+]: _______ of the molecule (minus one electron lost)
mass
Base peak: ______ peak in the spectrum (molecule in greatest abundance)
tallest
What are the 3 elements where Isostope ratios have distinctive appearance on MS?
1) C (100:1)
2) Cl (3:1)
3) Br (1:1)
What is the nitrogen rule in MS?
- an odd numbered molecular ion usually means that the unknown compound has 1 or 3 nitrogen atoms
- an even numbered molecular ion usually means that the unknown compound has 0 or 2 nitrogen atoms
Rank the 3 possiblilities for initial electron loss in order from highest energy to lowest energy
1) NB electron
2) pi electron
3) sigma electron
_______: the molecular ions may be unstable and will fragment
fragmentation patterns
_______ fragmentation: radical cation loses a small, neutral molecule (H2O)
type 1
In type 1 fragmentation, after the loss of an electron from the alcohol, it gains an H from the _______ carbon via homolytic cleavage
alpha
- one away
_______ fragmentation: the bond in the radical cation where the initial electron was lost breaks to give two molecules: a cation and a radical
type 2
type 2 fragmentation: the bond in the radical cation where the initial electron was lost breaks to give two molecules: a _______ and a _______
cation
radical
fragments that are _______ stable are more likely to exist
more
- C+ and C. stabilized by 3°>2°>1°>methyl
What are the common fragments lost in type 2:
1) CH3
2) CH3CH2
3) CH3CH3CH2
4) CH3CH3CH3CH2
1) 15
2) 29
3) 43
4) 57
In type two fragmentation, the MS gives _______-stablized cations whenever possible
resonance
_______ fragmentation: a bond elsewhere in the radical cation (often alpha), does homolytic cleavage yielding two molecules each with a radical
type 3
Type 3 fragmentation often yields an additional pi bond along with a ______ charged O or N
positively charged
a triple bond Oxygen+ (O+) connected to a Carbon is called a ________ ion
acylium
