Intro to Organic Chem Flashcards
What does bond order describe?
whether a covalent bond is single, double or triple
What is the bond order of a single, double, and triple bond?
single –> bond order = 1
double –> bond order = 2
triple –> bond order = 3
How many sigma bonds and/or pi bonds are found in a single bond?
1 sigma bond
How many sigma bonds and/or pi bonds are founc in a double bond?
one sigma and one pi
How many sigma bonds and/or pi bonds are found in a triple bond?
one sigma bond and 2 pi bonds
TRUE or FALSE: potential energy is directly proportional to bond strength.
FALSE –> potential energy is inversely proportional to bond strength
TRUE or FALSE: bond length is inversely proportional to bond strenght.
TRUE
What is the formula for formal charge?
formal charge = (# of valence electrons in free atom) - (# of electrons in lone pair) - (# of bonds)
TRUE or FALSE: In a Lewis diagram, the central atom is usually the least electronegative.
TRUE
What are 4 things to look out for when determining the MAJOR resonance structure?
- full octet
- minimum number of formal charges
- negative FC on electronegative atoms
- minimum separation between opposite FCs
What does VSEPR stand for?
valence shell electron pair repulsion
TRUE or FALSE: lone pairs contribute to the determination of the geometry of a molecule, using VSEPR theory.
TRUE
Provide the number of groups, bond angle(s), central atom hybridization for the following basic geometry:
Linear
(note: number of groups = number of atoms and lone pairs connected to the central atom)
number of groups = 2
bond angle = 180
hybridization = sp
Provide the number of groups, bond angle(s), central atom hybridization for the following basic geometry:
Trigonal planar
(note: number of groups = number of atoms and lone pairs connected to the central atom)
number of groups = 3
bond angle = 120
hybridization = sp2
Provide the number of groups, bond angle(s), central atom hybridization for the following basic geometry:
Tetrahedral
(note: number of groups = number of atoms and lone pairs connected to the central atom)
number of groups = 4
bond angle = 109.5
hybridization = sp3
Provide the number of groups, bond angle(s), central atom hybridization for the following basic geometry:
trigonal bipyramidal
(note: number of groups = number of atoms and lone pairs connected to the central atom)
number of groups = 5
bond angle = 90, 120
hybridization = sp3d
Provide the number of groups, bond angle(s), central atom hybridization for the following basic geometry:
octahedral
(note: number of groups = number of atoms and lone pairs connected to the central atom)
number of groups = 6
bond angle = 90
hybridization = sp3d2
TRUE or FALSE: each bond in a double bond contributes individually to the hybridization of an atom.
FALSE –> double bonds do NOT contribute individually to hybridization
If an atom has a choice between sp2 and sp3, it chooses _______.
sp2
What is the geometrical name for a molecule that has 2 groups and alone pair?
bent
What is the geometrical name for a molecule with 2 lone pairs and 2 groups?
bent
TRUE or FALSE: electron delocalization decreases a molecule’s stability.
FALSE: electron delocalization INCREASES a molecule’s stability
What is the name of the rule used to determine if a compound is aromatic? Provide the guidelines.
Huckel’s Rule…a molecule is aromatic if it is:
- planar
- cyclic
- fully conjugated (alternating single and double bonds)
- contains a total of 4n+2 pi electrons (where n = 0, 1, 2, 3, etc.)
note: all carbons must be sp2 hybridized
TRUE or FALSE: if an atom has both a lone pair and a double bond, the lone pair does not contribute to aromaticity.
TRUE –> note that the double bond contributes to aromaticity
TRUE or FALSE: if an atom has 2 lone pairs, both lone pairs contribute to aromaticity.
FALSE –> only one lone pair will contribute to aromaticity
Define chiral.
any object that CANNOT be superimposed on its mirror image
what are the 2 structural features of a stereogenic centre (chiral carbon)?
- the carbon will be sp3 hybridized (tetrahedral)
2. the carbon will be bound to 4 DIFFERENT atoms or groups
In a fisher projection, what is the difference between the vertical and horizontal lines?
vertical = going into the page horizontal = coming out of the page
What is a constitutional isomer?
structural isomers (different atom connectivity)
What is a stereoisomer?
isomer with same atomic connectivity, but different arrangement in space
What is a conformer/conformational isomer?
isomer with single bond rotation
Arrange the following from least stable to most stable conformer:
gauche
anti
eclipsed
eclipsed < gauche < anti
What letter of the alphabet designates a cis-alkene?
Z
What letter of the alphabet designates a trans-alkene?
E
If there are 3 substituents in an alkene isomer, how do you designate whether it is cis or trans?
Look for the higher priority group on each side of the double bond
What is an enantiomer?
mirror image that cannot be superimposed
i.e. same connectivity but opposite configuration at EVERY chiral centre
What are the 4 properties of enantiomers to keep in mind for the MCAT?
enantiomers:
- have opposite stereochemistry at ALL stereocenters
- have identical physical properties (bp, solubility, polarity)
- react identically in most environments
- react differently in a chiral environment
How must the lowest priority atom/group be arranged on a molecule, when designating R and S configuration of a chiral centre?
the lowest priority atom/group must be pointing into the page
Since enantiomers share identical physical properties, how can we tell them apart?
rotation of plane-polarized light
Define dextrorotary. Is it designated with (+) or (-)?
(+)
rotate plane-polarized light to the right (clockwise)
Define levorotatory. Is it designated with (+) or (-)?
(-)
rotate plane-polarized light to the left (counter-clockwise)
What is a racemic mixture?
a 50:50 mixture of 2 enantiomers
TRUE or FALSE: racemic mixtures result in a net rotation of plane-polarized light.
FALSE –> the 50:50 cancels out the rotation direction, so there is NO NET rotation
What is one method of separating racemic mixtures?
React the enantiomers with another chiral molecule to produce diastereomeric salts.
What are diastereomers?
stereoisomers that are not mirror images
must have at least one different stereocenter and at least one same stereocenter
How do you calculate the maximum number of stereoisomers that a given molecule can have?
2^n
n = # of chiral centers
What is a meso compound?
compound that contains a minimum of 2 chiral centers but is itself ACHIRAL
TRUE or FALSE: meso compounds rotate plane-polarized light
FALSE –> meso compounds do not rotate plane-polarized light
What are the 3 questions you should ask yourself when checking for meso compounds?
- Is there a minimum of 2 stereocentres?
- Is there a plane of symmetry?
- Are both halves of the molecule mirror images of each other (cannot be superimposed)?
Thin layer chromatography, paper chromatography, and column chromatography separate mixtures based on:
a) size
b) specific affinity
c) boiling point
d) polarity
e) charge
d) polarity
Gas chromatography separate mixtures based on:
a) size
b) specific affinity
c) boiling point
d) polarity
e) charge
c) boiling point
Size-exclusion separate mixtures based on:
a) size
b) specific affinity
c) boiling point
d) polarity
e) charge
a) size
Ion-exchange chromatography separate mixtures based on:
a) size
b) specific affinity
c) boiling point
d) polarity
e) charge
e) charge
Affinity chromatography, paper chromatography, and column chromatography separate mixtures based on:
a) size
b) specific affinity
c) boiling point
d) polarity
e) charge
b) specific affinity
What is the difference between stereospecific and stereoselective reactions?
stereospecific –> only create one kind of enantiomer
stereoselective –> favour one type of enantiomer, but still have some of amount of the other
What is the name of the extraction technique used to separate a mixture of enantiomers by producing diastereomeric salts?
resolution
In a liquid-liquid extraction, which layer is found on the top and which layer is found on the bottom? Describe the contents of the layers.
top = organic = large/less polar molecules
bottom = aqueous = small/more polar molecules, strong acids and bases, salts
b
