Ochem-2 Flashcards
What is the Grignard reagent?
It is an organometallic reagent that has the form R-Mg-X
View this reagent as a carbon anion ( -CH3 )
What do organo-metallic reactants do in a reaction?
They behave as very strong nucleophiles (acts like -CH3 even though that can’t actually be made) to help create C-C bonds
How do you make an organometallic compound?
Start with the alkyl halide ( H3C-Br ) and add the metal (Mg, Li, Cu) in an APROTIC solvent (like ether or THF)
You cannot react any of the Grignard reagents with anything that is protic (no water, no protic solutes or solvents), because the Grignard reagent will always go for the hydrogen first and then you won’t have any reagent left
What types of solutes and solvents can you not use with a Grignard reagent or an acetylide anion?
You CANNOT use protic anything
What is one major difference between hydration of an alkyne versus an alkene?
When hydrating an alkyne you don’t get a chance to further react with the product because of enol to keto tautomerization
Can you perform hydro-boration oxidation with an alkyne?
Yes, use (Sia)2BH and THF instead of BH3 and THF
What’s the only major synthesis reaction you can do with an alkane?
Free radical halogenation
Where can you form a resonance stabilized radical on an aromatic ring?
The allylic carbon (one bond away from a double bond)
If your goal is to add bromine in the allylic position on an aromatic ring what reagent should you use?
NBS (N-Br-succinimide), there is no Br2 so you only get the allylic product
With: light, or heat, or peroxide
What does benzylic oxidation mean?
You are oxidizing a carbon that is one carbon away from the benzene ring such that a Carboxylic acid is formed using that carbon
What is a requirement for a benzylic oxidation reaction with potassium permanganate?
There must be a benzylic hydrogen at the location of the benzylic carbon in order for that carbon to the oxidized (i.e. a quaternary carbon is completely unreactive)
In every EAS (Electrophile Aromatic Substitution) reaction what is the function of benzene?
It’s a Nucleophile
What will every electrophile that we use during an EAS reaction have with it?
A positive charge, because benzene is not a good nucleophile so you better be using a really good electrophile
In EAS reactions what activates benzene?
Electron donating groups, because benzene is acting as a nucleophile (nucleophile’s are electron donating groups, and if benzene has more electrons to donate it’s going to be more willing to donate those electrons, making it more reactive)
What are the two general steps of a general EAS reaction?
In with the new (the electrophile attaches), out with the old (the hydrogen is removed by a base, and the pi bond reforms)
What are the three forms of donating groups?
- -Nitrogen that has a lone pair that can donate by resonance
- -Oxygen that has lone pairs that can donate by resonance (even though nitrogen and oxygen are more electronegative than carbon, they are more donating due to resonance)
- -Methyl, ethyl, or propyl groups by hyperconjugation
How can you tell if a molecule is a withdrawing group?
It’ll have either a partial, or a full positive charge because it is bonded to more atoms than it would like, or it is bonded to several electronegative atoms
Which benzylic substituents are ortho/para directors?
All of the activating substituents, and the halogen withdrawing substituents
Which benzylic substituents are meta directors?
All of the deactivating substituents, except for the halogen substituents
If you have two substituents on a benzene ring, and one is a withdrawing group, and the other is a donating group, which one decides where a new substituent goes?
The donating group always wins, no matter how weak it is. Also, you cannot put a substituent directly between two other substituents due to sterics
What is a disproportionation reaction?
One in which oxidation and reduction happen in the same species of simultaneously
For E and Z naming, what is important about the type of substituents? (the location is also important, but you can only know if something is E or Z if you know something about the type and location of substituents)
The higher (heavier) functional group gets priority. For E, the highest priority groups on either side of the double bond must be trans to each other
What peak do you see just to the LEFT of the 3000 wave number in IR spectroscopy?
The sp2 C-H peak
What peak do you see just to the RIGHT of the 3000 wave number in IR spectroscopy?
The sp3 C-H peak
What could a peak at 3300 mean?
If it is accompanied by a peak at 2200, then it is a terminal Alkyne.
If not, it is an N-H group.
What functional group would a peak at 2200 signify?
If it is accompanied by a peak at 3300, then it is an alkyne.
If it is not, it is a nitrile group.
How can you distinguish an alkene in IR spectroscopy?
Look for the sp2 C-H group just to the LEFT of 3000, and also look for the small peak at 1650 (this is the C=C peak)
How can you distinguish an aromatic and IR spectroscopy?
Look for 1 or more peaks between 1500-1600, AND a peak just to the LEFT of 3000 for the sp2 C-H group
How can you distinguish an alcohol in IR spectroscopy?
Look for the broad, smooth peak/hill between 3200-3600
How do you distinguish a carboxylic acid in IR spectroscopy?
Look for the broad, UGLY peak between 2500-3500, AND the sharp carbonyl peak at 1700
How can you distinguish an aldehyde from a carboxylic acid in IR spectroscopy because they both have carbonyl peaks at 1700?
Look for the SISTER peaks at 2700 and 2800
Which standard isotopes are usually used in NMR?
Carbon-13 and Hydrogen
What shields and atom from a magnetic field?
The larger the electron cloud around the nucleus, the larger the electron cloud, and the greater the shielding
What does and an electronegative atom do to adjacent atoms shielding?
It pulls it away/reduces it
What reagents convert an alcohol into a ketone?
For a secondary alcohol, both PCC and Chromic Acid (Na2Cr2O7 / H2SO4) will do this
What reagents convert a ketone into an alcohol?
NaBH4 / EtOH
Where does the reagent carbon add in a Wittig reaction?
The carbon attached to the Phosphorous or the halogen will attach to the carbonyl carbon
What is an enamine?
An alkene and an amine sharing the same carbon
What is an imine?
C=N-R
It can be found in both chains and rings
What does hemi-acetyl mean?
- -The addition of alcohol to an aldehyde
- -Recognized by a single carbon being single-bonded to two hydroxide groups (OH) and ONE carbon atom
What does hemi-ketal mean?
- -The addition of alcohol to a ketone
- -Recognized by a single carbon being single-bonded to two OH groups and TWO carbon atoms
What is a ketal?
When two equivalents of oxygen bond to a ketone. The oxygens do not have hydrogens attached to them otherwise you would have a hemi-ketal.
–Recognize that the carbonyl carbon is the same carbon that attaches to both oxygens in the product
What does allylic mean?
This is the atom/molecule adjacent to a double-bond (as opposed to vinylic which is directed bonded to the double bond)
How does fractional distillation separate molecules?
Molecules are separated on the basis of BOILING POINT
How does thin layer chromatography separate molecules?
Based on polarity. The more polar the less distance that molecule will travel on the polarized silica gel.
What does PBr3 do in a reaction?
Converts alcohols into alkyl bromides
How do you add an alcohol to an alkene in the anti-markovnikov position?
- BH3 in THF
2. Peroxide, and -OH
How do you add an alcohol to an alkyne in the anti-markovnikov position?
- Sia2BH in THF
- Peroxide, -OH
Remember there is tautomerization
How do you add an alcohol markovnikov?
- HgSO4
2. H2SO4
When you attack an epoxide how do you know if you attack the more or the less substituted carbon?
If you are in acidic solution, you will have protonated the alcohol making it have a positive charge. You will then attack the more hindered carbon because it bears more of the positive charge.
In base you attack the least substituted side
What do you need to know about the Diels-Alder reaction?
You create two new sigma bonds from two pi bonds
