Organic Flashcards
With infrared spectroscopy, one absolutely needs to know three characteristic absorptions. One of those is alcohol, which has a __________ peak and absorbances at _________
Broad; 3300 cm -1
With infrared spectroscopy, one absolutely needs to know three characteristic absorptions. One of those is carboxyl in acid -OH group, which has a __________ peak and absorbances at _________
Broad; 3000 cm-1
With infrared spectroscopy, one absolutely needs to know three characteristic absorptions. One of those is a carbonyl group, which has a __________ peak and absorbances at _________
Sharp (deep); 1700 cm-1
With infrared spectroscopy, one absolutely needs to know three characteristic absorptions. One of those is N-H bond, which has a __________ peak and absorbances at _________
Sharp peak at 3300cm-1
When it comes to NMR on test day, counting the number of peaks and unique hydrogens may be enough but there are shifts to consider such as for alkyl groups: ________ppm
0 to 3
When it comes to NMR on test day, counting the number of peaks and unique hydrogens may be enough but there are shifts to consider such as for alkynes: ________ppm
2 to 3
When it comes to NMR on test day, counting the number of peaks and unique hydrogens may be enough but there are shifts to consider such as for alkenes: ________ppm
4.6 to 6
When it comes to NMR on test day, counting the number of peaks and unique hydrogens may be enough but there are shifts to consider such as for aromatics: ________ppm
6 to 8.5
When it comes to NMR on test day, counting the number of peaks and unique hydrogens may be enough but there are shifts to consider such as for Aldehydes: ________ppm
9 to 10
When it comes to NMR on test day, counting the number of peaks and unique hydrogens may be enough but there are shifts to consider such as for carboxylic acid: ________ppm
10.5 to 12
For NMR spectroscopy, what effect does electronegative groups have on the protons.
They pull electron density away from the protons causing it to be more deshielded and will result in the proton being further downfield
IR spectroscopy is most useful for distinguishing:
A) double and triple bonds
B) C-H bonds
C) Chirality of molecules ‘
D) relative percentage of enantiomers in mixtures
A) double bonds and triple bonds
Before absorbing an UV photon, electrons can be found in A) the HOMO only B) the LUMO only C) both the HOMO and the LUMO D) neither the HOMO nor the LUMO
A) the HOMO only
Wave number is directly proportional to _______
Frequency
In an IR spectrum, extended conjugated double bonds affects the absorbance band of carbonyl stretches compared with a normal absorption by how?
The absorbance band will occur at a lower wave number
What are the three intermolecular forces that affect solubility?
H bonds
Dipole-dipole interactions
Van der Waals (London) forces:
What are some examples of compounds that can do H bonding? And what will they move most easily into?
Alcohols or acids
Move most easily into the aqueous layer
List in order the forces that affect solubility that move most easily into the aqueous layer to least likely to move into the aqueous layer
Most likely: H bonding
Dipole-dipole
Least likely:Van der Waals
The water layer is called the ______. The nonpolar ether layer is called the ________
Aqueous phase (layer)
Organic phase (layer)
What piece of equipment is used in extractions?
Separatory funnel
It is more common for the organic layer to be on top but the denser layer will always be on the bottom
What is the “wash process”?
Small amount of solute is used to extract and remove impurities
What does filtration do?
Isolates a solid (residue) from a liquid (filtrate)
What is recrystalization
A method for purifying crystals in solution
What is the best way to separate two liquids with similar boiling points (less than 25 degrees Celsius apart)?
Fractional distillation
What method do you use when you want to distill a liquid with a boiling point over 150 degrees Celsius?
Vacuum distillation
What technique should only be used to separate liquids that boil below 150 degrees Celsius and have at least a 25 degree Celsius difference in boiling points
Simple distillation
How does chromatography separate compounds?
Based on how strongly they adhere to the solid, or stationary phase
*** how easily they come off into the mobile phase
What does thin layer chromatography (TLC) use for a stationary phase?
Silica gel, a highly polar substance
***any polar compound will adhere to the gel well and those move through (elute) slowly
What is the medium used for stationary phase for paper chromatography?
Cellulose
What is used as the mobile phase in TLC?
An organic solvent of weak to moderate polarity so it doesn’t bind well to the gel.
Nonpolar compounds dissolve in the organic solvent and move quickly as the solvent moves up the plate, where as the more polar molecules stick to the gel,
Thus the more nonpolar the sample, the farther up the plate it’ll go
Explain the reverse phase chromatography technique with the stationary phase
The stationary phase is nonpolar so polar molecules move up the plate quickly while nonpolar molecules stick more tightly to the stationary phase.
*** the exact opposite of TLC
When TLC is performed, how are compounds generally identified?
Using the retardation factor (Rf)
Which is the distance spot moved divided by the distance solvent front moved
What are the principles behind column chromatography?
1) uses an entire column filled with silica or aluminum beads as an absorbent (allows for better separation)
2) uses gravity to move the solvent and compounds down the column
3) the more similar the sample is to the mobile phase, the faster it elutes it and vice versa
What technique can be used to separate and collect macromolecules such as proteins or nucleic acids?
Column chromatography
What type of chromatography are the beads in the column coated with charged substances so that they attract or bind compounds that have an opposite charge?
Ion-exchange chromatography
What is the mechanism of ion exchange chromatography ?
The beads in the column are coated with charges so when something comes through the column it’ll bind to those oppositely charged beads. Then to release the bound DNA or proteins use a salt gradient to elute the charged molecules that have stuck to the column
What type of chromatography has beads in the column that contain tiny pores of varying sizes that allows small compounds to enter the beads and the larger molecules to travel through the column faster?
Size-exclusion chromatography
What is a common approach to protein purification?
Use an ion exchange column followed by a size-exclusion column
When would one use affinity chromatography? Similar to his-tagging of proteins
When you want to bind a protein of interest to the column that has high affinity for that protein
Stationary phase commonly used for this is Nickel which is commonly used in mechanisms like his-tagging proteins
What are characteristics of volatile compounds
They have low melting point, sublimate solids or vaporizable liquids
What is the mechanism of gas chromatography?
The volatile sample is injected into the column and moves with the gaseous mobile phase through a stationary liquid or solid phase; a computer identifies the components
What does mass spectroscopy involve?
The ionization and fragmentation of compounds
These fragments are then run through a magnetic field, which separates them by their mass to charge ratio
The total molecular weight can thus be determined
What is the HPLC elutent? And what is the mechanism of HPLC?
Elutent is a liquid
A small sample is injected into the column and separation occurs as it flows through
The compounds pass through a detector and are collected as the solvent flows out of the end of the apparatus.
What are the similarities and differences in HPLC and gas chromatography
Similarities: the entire system is computerized
Differences: uses liquid pressure instead of gas
What are structural isomers
Share the same molecular formula but have different structures
What re examples of physical properties and what are physical properties?
No change in composition of matter
Ex: melting point, boiling point, solubility, odor, color, density
What are conformational isomers? And how are they best visualized?
Differ in formation around single (sigma bonds)
Arise from the fact that varying degrees of rotation around single bonds can create different levels of strain
Newman projection
What are the Newman projection names in order from lowest energy level (most stable) to highest energy level (least stable)
Lowest energy level: staggered conformation (anti conformation, two largest groups are farthest away from each other)
–eclipsed: two largest groups are 120 degrees apart
- gauche: two largest groups are 60 degrees apart
- totally eclipsed: two largest groups are on top of each other (0 degrees apart) Highest energy (least stable)
What makes an object chiral?
If this mirror image cannot be superimposed on the original object (there is a lack of an internal plane of symmetry
What are enantiomers?
Non superimposable mirror images that have the same connectivity but opposite configurations at every chiral center in the molecule
Have identical physical and chemical properties except they have different optical activity and reactions in chiral environments
What are diastereomers?
Non-mirror-image configurational isomers
Occur when a molecule has two or more stereogenic centers and differs at some but not all of these centers
Diastereomers are required to have multiple chiral centers. So for an molecule with “n” chiral centers, there are 2^n possible stereoisomers
Stereoisomers that are mirror images of each other are __________. Stereoisomers that are not mirror images of each other are _____________.
Enantiomers
Diastereomers
Diastereomers have what properties?
Have different chemical properties but may behave similarly in some reactions because they have the same functional groups
They are arranged differently in space so will consistently have different physical properties.
Cannot rotate plane polarized light
What is the definition of cis-trans isomers?
A specific subtype of diastereomers in which substituents differ in their position around an immovable bond such as a double bonds or a cyclic ring structure
What are Meso compounds?
Molecules that have chiral centers and have an internal plane of symmetry
What two things must a molecule have in order to have optical activity?
Must have chiral centers within it and must also LACK a plane of symmetry.
If there is an internal plane of symmetry, then the molecule is not optically active
What does configuration mean and what are the definition of the two types of configurations, relative and absolute?
Configuration of a stereoisomer refers to the spatial arrangement of the atoms or groups in the molecule
Relative configuration of a chiral molecule is its configuration in relation to another (often through chemical inversion)
Absolute configuration: of a chiral molecule describes the exact spatial arrangement of these atoms or groups, independent of other molecules
When is E and Z nomeclature used? And how is priority set?
Used for compound with polysubstituted double bonds
Priority based on the highest atomic number
If the two highest priority substieutents on each carbon are on the same side of the double bond then that is termed Z
If they are on opposite sides then it is termed E
What are the steps in determining R and S forms?
1) assign priority based on highest atomic number
2) invert the stereochemistry by moving the lowest priority to the back of the molecule. *** but with that remember to switch the final configuration to the opposite to compensate
3) Draw a circle connecting from 1 to 2 to 3 of the priorities. If the circle is clockwise it is called R. If the circle is counterclockwise it is called S
What do R and S help determine?
The absolute configuration at a chiral center
When will an acid base reaction proceed?
If the products that will be formed (conjugate acid and conjugate base) are weaker than the original reactants
When do coordinate covalent bonds occur?
When Lewis acids and bases interact
Water acts as a base in a(n) _________ solution
Water acts as a acid in a(n) ________ solution
Acidic solution
Basic solution
What range are the pKa s for acids, bases, weak organic acids?
Acidic molecules will have a smaller (or even negative) pKa
Mor basic molecules will have a larger pKa
Acids with pKa ‘s below -2 are considered strong acids an completely dissociate in aqueous solutions
Weak organic acids often have pKa values between -2 and 20
Bond strength relationship to acidity?
What is electronegativity relationship to acidity?
Bond strength decreases down the periodic table, acidity therefore increases
The more electronegative an atom, the higher the acidity
*** when these two trends oppose each other, low bond strength takes place
What functional groups act as acids?
Alcohols
Aldehydes and ketones at the alpha carbon (carbon adjacent to the carbonyl)
Carboxylic acids and most carboxylic acid derivatives
** these are easy to target with a basic (or nucleophilic) reactants bc they readily accept a lone pair
What functional groups act as bases?
Amines and amides
*** Amines are capable of forming coordinate covalent bonds by donating a lone pair to a Lewis acid
Good nucleophiles tend to be good _______
Base
What do nucleophiles tend to have? And what key elements should you keep an eye out for on test day that are key in identifying them.
Lone pairs or pi bonds that CN be used to form covalent bonds to electrophile
** Look for Carbon, Hydrogen, Oxygen, or Nitrogen on test day
How is nucleophilicity affected by:
Charge?
Electronegativity?
Steric Hindrance?
Solvent?
Charge: nucleophilicity increases with increasing electron density
EN: nucleophilicity decreases as EN increases
Steric Hindrance: bulkier molecules are less nucleophilic
Solvent: Protic solvents hinder nucleophilicity by protesting nucleophile or through H bonding
What are aprotic solvents? And what are some examples?
Aprotic solvents cannot hydrogen bond
DMF, DMSO, acetone
What are common examples of protein solvents? And what are protein solvents?
Protect solvents can H bond
Examples: carboxylic acids, ammonia/ amines, water/ alcohols
In polar protic solvents, what is the nucleophilicity of the halogens in from most to least
I-,Br-,Cl-, F-
In polar aprotic solvents, what is the nucleophilicity of the halogens from most to least
F-, Cl-, Br-, I-
What is an electrophile and what is an example of a really good one?
Electrophiles will almost always act as Lewis acids in reactions
A greater degree of positive charge increases electrophilicty
How are electrophilicity and acidity related?
Essentially identical when it comes to reactivity.
Just as alcohols, aldehydes and ketones, carboxylic acids and their derivatives act as acids, they also act as electrophiles and can make good targets for nucleophilic attack
The more substituted a carbon is the more likely _______ reaction will happen
The less substitieuted the carbon is the more reactive it is in ________ reactions
SN1 and SN2 reaction comparison
SN1
SN2
What does O3, then Zn form when reacted with and Alkene?
Aldehyde and a ketone
What results when an alkene is reacted with O3 then H2O2?
Carboxylic acid and a ketone
What results when you react an alkene with OsO4 or KMnO4,OH-?
Vicinity idol formation
Alcohols are readily oxidized to carboxylic acids by any oxidizing agent other than ________, which will only oxidize primary alcoholic to _________.
PCC
Aldehydes
What are mesylates and how are they prepared?
A compounds containing the functional group -SO3CH3
They are prepared using methylsufonyl chloride and an alcohol in the presence of a base
what are two subgroups of stereoisomers?
conformational
configurational
what are conformational stereoisomers?
simple rotation of a sigma bond
no bond breaking
same connectivity
same substituents
what are configurational stereoisomers?
bond breaking required
same connectivity
same substituents
what are constitutional isomers?
different elements
bond breaking necessary
connectivity is different
different names
configurational isomers have two branches. what are those two branches?
optical isomers
cis/trans isomers
if there are no cis/trans isomers and they are configurational isomers then they are ______
optical isomers
what are the two branches of optical isomers?
enantiomers
diastereomers
how do enantiomers differ?
1) rotation of plane polarized light
2) behavior in chiral environments
what are enantiomers?
configurational isomers that are nonsuperimposabe mirror images of eachother. contain chiral center(s)
what are diastereomers?
configurational isomers with MORE THAN one stereocenter that are nonsuperimposable and NOT mirror images
what are the possible subtypes of configurational isomers?
cis-trans isomers
optical isomers: enantiomers and diastereomers
