Organic Chemistry - TPR Review Questions Flashcards
Explain the difference between sigmaandpi bonds
Sigma: single bonds (result of end-to-end overlap of orbitals)
Pi: double bonds and triple bonds (result of side-to-side overlap of orbitals)
Explain the difference between sp-, sp2-, and sp3-hybridized carbon atoms
sp-
two groups bonded 180 degrees apart
sp2-
three groups bonded 120 degrees apart
sp3-
four groups bonded 109.5 degrees apart
Name three functional groups that have delocalized electrons
All carbonyl containing groups:
Ester
Amide
Carboxylic Acid
Acid Anhydride
Acid Halide
Aldehyde
Ketone
To what term does unsaturated refer to
An unsaturated molecule contains one or more rings or a pi bond resulting in less than maximum hydrogens
Rank the four possible types of alky carbocations from least stable to most stable:
(least)
Unsubstituted (methyl)
Primary
Secondary
Tertiary
(most)
What must be present for resonance to occur?
A pi bond so that electrons can be delocalized
What is a chiral center?
A carbon atom bearing 4 different substituents
Explain the difference between:
structural isomers
conformational isomers
stereoisomers
structural isomers
two molecules with same molecular formula but different connectivities
conformational isomers
same molecular formula but differ in rotations about single bond
stereoisomers
same molecular formula, same connectivities, but groups differ in spacial arrrangements in molecule
What is a different name for geometric isomers?
Geometric isomers are a type of diastereomer. They can also be referred to as cis/trans isomers about a double bond or ring.
What are the two types of stereoisomers?
What are the differences?
geometric isomers
optical isomers
What is the most stable conformation of methylcyclohexane?
The chair form with an equatorial methyl group
What is a racemic mixture?
A mixture of enantiomers that are in equal proportions (50/50) and thus do not reflect plane polarized light (no optical activity)
What is a nucleophile?
What is an electrophile?
A nucleophile is a species that is electron rich and is attracted to something that is electron deficient to donate a pair of electrons to. It usually has either a full or a partial negative charge associated with it and/or a lone pair of electrons.
An electrophile is a species that is electron deficient, so it is attracted to an electron rich species. It usually has either a full or partial positive charge associated with it.
What is a Lewis Acid?
What is a Lewis Base?
A Lewis Acid is an electron-pair acceptor (or an electrophile)
A Lewis Base is an electron-pair donor (or a nucleophile)
What is a leaving group? What makes something a good leaving group?
A leaving group is a stable species that detaches itself from a molecule with its electron pair during the course of a reaction
Is inversion of configuration seen in an SN1 or an SN2 reaction? Which yields a racemic mixture of products?
An inversion of configuration is seen in an SN2 reaction; and an SN1 reaction yields a racemic mixture
Why?
WIll a more substituted substrate favor the SN1 or the SN2 mechanism?
SN1, because the first step is the formation of a carbocation, and more substituted carbocations are more stable
Is the rate of the SN1 or the SN2 mechanism dependent on the nucleophile concentration? Choose one.
The SN2 mechanism is dependent on the rate of the nucleophile concentration
Why? Why isn’t the SN1?
What types of isomers are tautomers?
Tautomers are structural isomers
Tautomers are isomers of a compound which differ only in the position of the protons and electrons. The carbon skeleton of the compound is unchanged. A reaction which involves simple proton transfer in an intramolecular fashion is called a tautomerism.
What is an acetal? What is a hemiacetal?
Acetals contain two –OR groups, one –R group and a –H atom. In hemiacetals, one of the –OR groups in acetals is replaced by a –OH group.
Hemiacetal is an intermediate chemical compound formed during the chemical process of acetal formation. Therefore, these two groups have a slight difference in their chemical structure. In detail, the central carbon atom in both of these compounds is a sp3-C atom bonded to four bonds, and out of these four bonds, only one bonding type is different.
Fill in the blanks
Fill in the blanks (acetal/hemiacetal)
Fill in the blanks (acetal and hemiacetal formation)
FIll in blanks (acetal/hemiacetal)
Fill in blanks (acetal/hemiacetal)
What is a hydride? How does it differ from a proton? How does it differ from a hydrogen atom?
A hydride is H:-
A proton is H+
A Hydrogen is H•
(the hydrogen atom is a hydrogen radical)
What is an imine?
An imine is a the nitrogen equivalent to a ketone or aldehyde
NCRRR or NHCRR
What type of mechanism is the saponification of a triglyceride?
Saponification is an addition-elimination reaction
Name the carboxylic acid derivatives from least to most reactive:
(Least Reactive)
amide
ester
acid anhydride
acid halide
(Most Reactive)
Give the approximate infrared stretching frequencies for the following functional groups:
a) O-H
b) C=O
c) C=C
a) O-H - 3200-3600 cm-1
b) C=O - 1700 cm-1
c) C=C - 1650 cm-1
What structural information does an infrared spectrum show?
The functional groups present in a molecule
What does splitting in a 1H NMR spectrum indicate? What does the number of signals in the spectrum show?
Splitting: the number of nonequivalent hydrogens on adjacent carbon atoms;
Number of Signals: The number of nonequivalent hydrogens in the molecule
Are molecules with five or fewer carbon atoms that also bear a polar functional group more soluble in the aqueous or the organic layer in an extraction?
They are more soluble in aqueous layer
(think of something with 5 or fewer carbon atoms and a polar group as something that is polar, therefore it would interact with water better)
What functional groups can be manipulated in an extraction to alter the solubility of a molecule?
Carboxylic acids
Phenols (ArOH)
Amines
Do polar molecules or nonpolar molecules have lower Rf values in a TLC experiment?
Rf = distance traveled by solute/distance of solvent front
Polar molecules have lower Rf values
The stronger a compound is bound to the adsorbent , the slower it moves up the TLC plate. Non-polar compounds move up the plate most rapidly (higher Rf value), whereas polar substances travel up the TLC plate slowly or not at all (lower Rf value).
For each of the following chromatographic techniques, name the property or properties that is (are) key to the function of this technique:
a) TLC
b) GC
c) SEC
d) affinity chromatography
e) ion-exchange chromatography
a) TLC - Polarity
b) GC - Polarity and Boiling Point
c) SEC - Size
d) affinity chromatography - IMF (intermolecular forces)
e) ion-exchange chromatography - Charge and Size
Using R for the side chain, write the general structure of an amino acid.
(see image)
Are animal amino acids in the D or in the L configuration?
In the L-Configuration
What are two common techniques used to synthesize amino acids?
The Strecker and Gabriel-malonic ester syntheses
(mcat-review.org says no longer a topic on MCAT. Double check this…)
Which of the two functional groups of an amino acid is more basic?
The amino group
What is the pKa of the carboxylic acid of an amino acid?
Carboxylic acid is ~ 2
Amino is ~ 10
What are the two common names for the bond linking two amino acid residues together in a protein?
Amide Bond
Peptide Bond
In carbohydrates, in their pyranose form, the anomeric carbon is part of what functional group?
The anomeric carbon is part of a hemiacetal
