dat organic chemistry: 1H NMR, IR, mass spectroscopy Diagram | Quizlet

mass spectrometry is an analytical tool used to determine...

the MASS of a molecule lol

mass spec: we take a pure sample of the compound (random mass) and do what with it?

vaporize it and fragment it into a bunch of ions

what happens to the ions in the mass spectrometer?

(guided from where to where, and how?)

the charged molecules are guided by electromagnetic attraction or repulsion (depending on m/z) to a detector mechanism

what does a mass spectrum plot?

(what does the detector tell us?)

a mass spectrum plots the different mass-to-charge ratios (m/z) against their "relative abundances" within the sample (how many of that ion did the sample have?).

mass spec: the taller the peak....

the greater abundance of the corresponding fragment.

but on what scale are we quantifying the mass spec peaks? is it straight up # of occurrences?

not exactly. rather, the intensity of the peaks is set RELATIVE to the tallest peak (most abundant ion) in the entire spectrum: the base peak. this corresponds to the most stable molecular fragment.

abundance is a %

where can we find the molecular ion peak (mass spec)?

it is typically a high peak with the highest m/z ratio (rightmost on the X axis). note that the base peak and molecular ion peak are often NOT the same peak.

what type of spectroscopy is commonly used to identify the functional groups present in a molecule?

infrared (IR) spec

an IR spectrum is acquired when an organic molecule vibrates upon exposure to infrared radiation. for vibrations to occur for a given bond, it MUST....

have a NET DIPOLE MOMENT

IR: does C-OH have a net dipole moment? what about O=O? what about C2H4 (C=C)?

C-OH yes

O=O no

C=C no

fully symmetrical bonds don't have a net dipole moment and don't show up on the IR spec

IR spec:

x-axis

y-axis

x-axis: wavenumber (cm^-1) (proportional to energy)

y-axis: % transmittance (how much light was absorbed by the detector)

IR spec: a low % transmittance implies what? wb high?

if the detector absorbed a lot of light (high %T), then the sample/expected functional group didn't (so it "doesn't exist" from the pov of the detector).

but if the detector didn't absorb a lot of light (low %T) at a given wavelength, this means the functional group did instead, meaning it definitely exists

mass spec: but what actually tells us the mass of the original, unfragmented compound? do we combine the peaks or something?

NO: there is ONE peak we are looking for. it is called the molecular ion peak, and it represents the entire molecule in question, prior to any fragmentation. the M/Z ratio of this peak IS the mass of the original molecule.

overall range of IR spec

0-4000

TERM

single bond to H!!! region

DEFINITION

single bonds to H region (2500-4000)

TERM

triple bond region

DEFINITION

triple bond region (2000-2500)

TERM

double bond region

DEFINITION

double bond region (1500-2000)

TERM

secondary amine

DEFINITION

3200-3500

secondary amine: ONE peak

R2-NH bc one N-H bond

TERM

primary amine

DEFINITION

3200-3500

primary amine: TWO peaks

R-NH2 bc two N-H bonds

TERM

sp3 CH

DEFINITION

sp3 CH: just RIGHT of 3000

can pretty much ignore this peak since it shows up at every spectroscopy

TERM

sp2 CH

DEFINITION

sp2 CH: just LEFT of 3000

can pretty much ignore this peak since it shows up at every spectroscopy

TERM

NO2 nitro

DEFINITION

NO2 nitro

vampire teeth 1500, 1400

TERM

carbonyl

DEFINITION

carbonyl 1700 ish long peak

TERM

-OH thats a part of acid (COOH)

DEFINITION

-OH thats a part of acid (COOH)

2500-3500 BROAD JAGGED PEAK

TERM

-OH (not part of acid)

DEFINITION

-OH (not part of acid)

3200-3500 large broad smooth peak

TERM

nitrile C≡N

DEFINITION

nitrile C≡N

2200-2250

medium peak

TERM

aromatic

DEFINITION

aromatic:

squiggly tiny peak in btwn double and triple bond region

medium peak btwn double and fingerprint region

long peak in fingerprint region ~1000

TERM

C=C alkenes or C=N imines

DEFINITION

C=C alkenes or C=N imines ~1600

TERM

fingerprint region

DEFINITION

fingerprint region

before 1500

what is 1H NMR spectroscopy?

(goal, measure what signals?)

- used to determine the molecular structure of a compound

- measures the signals produced by different protons (hydrogen atoms) in a molecule when exposed to a magnetic field

1H NMR: what does each signal represent?

(we already said proton.... think deeper)

signals correspond to protons in "different chemical environments."

equivalent protons (in the same chemical environment) produce the same signal, so they contribute to the same peak!!

only non-equivalent protons (in different environments) produce distinct signals.

1H NMR: what does the number of signals tell us?

# of sets of non-equivalent protons in a molecule.

For example, methyl acetate has two signals because it has two sets of protons in different environments.

1H NMR: what does symmetry do?

Symmetry can make protons chemically equivalent, even if they are attached to different carbons.

Example: In bromobenzene, the molecule's symmetry results in only three signals despite having five protons.

1H NMR: what is chemical shift?

when, due to electron shielding, the peak shifts from its expected place for a specific type of grp

1H NMR: chemical shift

deshielded protons (less electron density), ex near EWG/en groups, appear _____field (further __________).

shielded protons (more electron density) _____field (further __________).

1H NMR: chemical shift

deshielded protons (less electron density), ex near EWG/en groups, appear DOWNfield (further LEFT).

shielded protons (more electron density) UPfield (further RIGHT).

1H NMR: what is "signal multiplicity"?

refers to the number of peaks within a signal, caused by non-equivalent neighboring protons.

1H NMR: what is a "neighboring non-equivalent proton"?

on the atom directly adjacent!!!!!!!

1H NMR: the number of peaks (multiplicity) with in a signal = ?????

(special rule!!!)

n+1 rule: # of peaks = number of neighboring non-equivalent protons (n) + 1

Example: In 2-butanone:

- Methyl group protons (–CH3) have no neighbors → singlet (1 peak).

- CH2 protons have 3 neighbors → quartet (4 peaks).

- CH3 protons have 2 neighbors → triplet (3 peaks).

1H NMR: what is signal integration?

relative # of protons giving rise to each signal

GIVEN TO US

Example: If signal A has twice the integration of signal B, there are twice as many protons contributing to signal A.

1H NMR: what does the height of the peak represent?

upfield (closer to 0, far right) means more electron density. downfield (further from 0, far left) means less electron density.

rank the following, guessing at 0-14 range

- sp3 C-C-H

- sp2 C=C-H

- R-(C=O)-OH

- aromatic-H

- Ph-OH

- R-(C=O)-NH

- R-C-OH, R2-NH

- R-(C=O)-H

(1) sp3 C-C-H (~0.5–2 ppm) - most shielded, high electron density.

(2) R-C-OH, R2-NH (~2–5 ppm) - moderately deshielded by electronegative O/N.

(3) sp2 C=C-H (~4–6.5 ppm) - slightly deshielded by double bonds.

(4) Ph-OH (~4–8 ppm) - Phenol group deshields.

(5) aromatic-H (~6–8 ppm) - Deshielded by ring current effect.

(6) R-(C=O)-NH (~6–9.5 ppm) - Amide, moderately deshielded by carbonyl (since it's separated by 1 atom) and N.

(7) R-(C=O)-H (~9–10 ppm) - Strong deshielding due to aldehyde H being directly on carbonyl C.

(8) R-(C=O)-OH (~11–14 ppm) - Highly deshielded due to carboxyl group.

1H NMR: ethyl

quartet and triplet

1H NMR: isopropyl

septet and doublet

1H NMR: tert-Butyl

singlet

which protons count for 1H NMR?

any, whether they r connected to O, C, N, etc

Which of the following compounds would contain a peak at m/z = ______?

notice if there is a weaker C-C bond that seems prone to breaking off - if heres basically a full functional grp of that particular m/z

aromatic group mass

propane mass