MCAT: Foundation 5

Arrhenius acid

substances that dissociate in water to give H3O+ ions

3:2:2:2

butyl integration HNMR

1:2:3:3

isobutyl integration HNMR

1:1:1:1

tertbutyl integration HNMR

Arrhenius base

substances that dissociate in water to give OH- ions

greater degree than weaker acids

stronger acids dissociate at a

weaker acids

stronger acids dissociate more than

conjugate acid

when a base accepts a proton, it becomes an acid capable of returning that proton

conjugate base

when an acid donates a proton, it becomes a base capable of accepting that proton back

a weaker acid and a weaker base

the acid-base equilibrium favors

larger the pKa

the weaker the acid the

the larger the pKb

the weaker the base the

pKa electronegativity effect

the more electronegative element bears a negative charge more easily, giving a more stable conjugate base and a stronger acid

as size increases so does the acidity

pKa size effect

stabilize the conjugate base and increase acidity more than a single group

multiple electron withdrawing groups can

hybridization on acidity

as the hybridization decreases the acidity increases

resonance on pKa

more delocalized more acidic

lewis bases

electron pair donor (nucleophile)

nucleophile

donates electrons to a nucleus with an empty orbital, An electron-pair donor

lewis acids

electron pair acceptor (electrophile)

electrophile

accepts a pair of electrons

alkanes

single bonds between the carbons, all carbons are sp3, no functional groups

cycloalkanes

sp3 carbons form a ring

alkene

hydrocarbons that contain carbon-carbon double bonds and ends in (-ene) sp2

cycloalkene

double bond in a carbon ring

alkynes

hydrocarbons that contain carbon-carbon triple bond

aromatic hydrocarbons

derivatives of benzene (arenes)

alcohols

contain the hydroxyl group (-OH) as the functional group

ethers

contains two alkyl groups bonded each to oxygen

aldehydes

a double bond with oxygen (carbonyl group) and a single bond with another element

ketone

an organic compound with a carbonyl group attached to two carbon atoms

carboxylic acid

contain the carboxyl group, each derivative contains a carbonyl group and a bond with an electron-withdrawing group

amine

alkylated derivatives of ammonia

amides

carboxylic acid derivative with a nitrogen attached to the carbonyl group

nitriles

contain the cyano group

ester

C=O(O)R

alkyl halide

carbonyl

carboxyl

sulfide

thiol

thioester

hydroxyl

isopropyl group

2 branches

brønsted–lowry acid

proton donator

brønsted–lowry base

proton acceptor

as atomic mass increases

Frequency decreases…

as bond energy increases

Frequency increases…

sp3 carbon-carbon single bond stretch

1000-800 cm-1

sp2 carbon-carbon double bond stretch

1650-1600 cm -1

sp carbon-carbon triple bond stretch

3300 cm -1

Alcohol O-H stretch

(3300 cm-1) broad with a rounded tip

Acids O-H stretch

(2500-3300 cm -1) very broad

Primary amine (RNH2) stretch

(3300 cm-1) broad with two sharp spikes

Secondary amine (R₂NH) stretch

(3300 cm -1) broad with one sharp spike

Tertiary amine (R₃N) stretch

no signal because no H-bonds

alkane IR

only C-H and C-C bending frequencies

C-H stretch

broad band between 2800 and 3000 cm–1, present in almost all organic compounds

Isolated C=C frequency

1640-1680 cm -1

Conjugated C=C frequency

1620-1640 cm -1

aromatic C=C frequency

approx. 1600 cm-1

unsymmetrical

for a C=C signal the signal must be…

benzene common frequency

1619 cm -1

unsaturated =C-H

just above 3000 cm -1

unsaturated -C-H

just below 3000 cm -1

fingerprint region bonds

C-C, C-O, C-N (indetectable)

C=C stretch

1600-1690 cm -1

internal alkyne stretch

no detectable signal due to symmetry

external alkyne stretch

just below 2200 cm -1

carbon-nitrogen triple bond stretch (nitrile)

(2200 to 2300 cm–1) intense and sharp absorption

so nitriles produce stronger absorptions than alkynes.

Nitrile bonds are more polar than carbon–carbon triple bonds…

common C=O stretch

1710 cm –1, usually strongest signal in IR

ketone C=O stretch

around 1710 cm-1

ketone IR

C=O around 1710 cm-1 and saturated C-H just below 3000 cm-1

aldehyde IR

C═O stretch around 1720 cm –1 and two different stretch bands for the C-H bond at 2720 and 2820 cm –1

aldehyde C=O

1725 cm -1

carboxylic acid C=O

1710 cm-1

carboxylic acid IR

O-H absorbs broadly (2500-3500 cm-1) due to strong hydrogen bonding and C=O around 1710 cm-1, need both peaks

saturated aliphatic carboxylic ester C=O

from 1750-1735 cm -1

α, β-unsaturated carboxylic ester C=O

from 1730-1715 cm -1

α, β-unsaturated carboxylic ester IR

C=O from 1730-1715 cm -1 and numerous C-O peaks and two alkyl C-H peaks

saturated aliphatic carboxylic ester IR

C=O from 1750 to 1735 cm-1 and a few C-O peaks with one alkyl C-H peak

ether IR

The C—O stretch is in the fingerprint region around 1000–1200 cm –1, has C—O stretch but does not have a C═O or an OH stretch, then the compound

C-O stretch

1000 to 1300 cm-1

amide absorption

C═O at 1640 - 1680 cm –1, N-H absorptions around 3300 cm -1

MS fragmentation

The masses of the fragments and their relative abundance reveal information about the structure of the molecule, only positive signals are detected

radical ion

when a molecule loses one electron, it then has a positive charge and one unpaired electron

most common mass spectrometer

magnetic deflection

m/z

the exact radius of curvature of an ion's path depends on its mass-to-charge ratio (+1)

base peak

the tallest peak, 100% abundance most common fragmentation

M+ peak

molecular ion peak; corresponds to molecular weight

methyl m/z

15

ethyl m/z

29

propyl m/z

43

butyl m/z

57

pentyl m/z

71

benzene m/z

78

High Resolution MS

the exact mass of a compound can be found

isotopes are present in their usual abundance

MS with isotopes

Br MS

79 Br (50.5%) and 81 Br (49.5%) M+ peak and an M+2 peak of equal height