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What is the equation for aromaticity?
4N+2
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What is the equation for anti-aromaticity
4N
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What are the two majors types of reactions during retrosynthesis?
Functional group change, formation of new C-C bond and/or breaking of C-C bonds
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Asymmetrical synthesis
Synthesis in which only a desired stereoisomer is produced
To achieve this, use either a stereoselective or stereospecific reaction at the step in which more than one isomer could be made
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What 4 things should be provided for each synthetic step?
Overall reactants, reagents added, reaction conditions, overall products
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Where are the reagents located on the synthesis arrow, and where are the reaction conditions?
Reagents are on top of arrow, reaction conditions are below
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Enantioselective synthesis
A mix in which one enantiomer is found in greater proportion than the other.
Requires a chiral reagent or catalyst to create a chiral environment to take place in
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Linear synthesis
A synthesis composed of sequential steps
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Convergent synthesis
Portions of the target are assembled separately and then assembled together at later stages
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What makes one synthesis better than another?
Less costly, more environmentally friendly
Ideally: decrease the number of steps while increasing the percent yield for each step
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12 Principles of green chemistry
- Waste prevention
- Atom economy
- Less hazardous chemical synthesis
- Safer solvents and auxiliaries
- Design for energy efficiency
- Use of renewable feedstocks
- Reduce derivatives
- Catalysis
- Design for degradation
- Real-time pollution prevention
- Safer chemistry for accident prevention
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The three types of green chemistry that we focus on:
- Less toxic reagents/solvents
- Ex: using a reagent that will be less damaging to the environment
- Safer reaction conditions:
- Creating reactions that will create safer alternative byproducts
- Efficiency and atom economy:
- Maximizing the percent yield of a reaction can prevent side products from being released into the environment
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How to calculate % atom economy
Mass of atoms in the desired product/mass of atoms in all reagents *100%
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Double bonds are more thermodynamically stable when they're ___ than ___
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The more stable the compound, the ___ heat released during hydrogentation
Less
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For conjugated double bonds, the heat of hydrogenation is ___ than the sun for the individual bonds
Less
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Resonance energy for aromaticity
The difference between the predicated energy and the observed value
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What are the requirements for aromaticity
- Structure must be cyclic with conjugated pi bonds
- Each atom in the ring must have an unhybridized p orbital (sp2 or sp)
- The p orbitals must overlap continuously, indicating planarity
- Delocalization of the pi electrons over the ring must lower the electronic energy
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Frost method
Useful for determining the MO diagrams of fully conjugated, cyclic pi systems
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Steps to the frost method
- Draw the polygon that represents the structure so that one of the vertices is pointing directly downward
- Place any non-bonding orbitals in the middle of the polygon
- Place the energies of the bonding/anti-bonding orbitals at the vertices of the polygon
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Naming annulenes
One ring molecules that contain only carbon and hydrogen and have alternating double and single bonds
Named [n]annulene where the n= amount of carbons in the ring
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How many pi bonds are in a triple bond
2 pi bonds
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Nucleophilic attack at carbonyl carbons tends to be more energetically favorable for _____ than _____
Aldehydes than ketones
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Adding NaBH4 to a ketone yields
A secondary alcohol
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Adding NaBH4 to an aldehyde yields
A primary alcohol
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Adding LiAlH4 (LAH) to a ketone yields
A secondary alcohol
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Adding LiAlH4 (LAH) to an aldehyde yields
A primary alcohol
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At slightly basic pH NaBH4 ____ deprotonates water and alcohols
Slowly
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LAH ____ deprotonates weakly acidic protons from water and alcohol, creating H gas and heat
Rapidly
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A reduction reaction will increase the number of ___ bonds and decrease the number of ___ bonds
C-H
C=O
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LAH and BH4 react in ways that create ____ reactions
reduction
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Grignard reagents act as both
Strong nucleophiles and strong bases
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Witting reaction (Ylide)
Reacts with a ketone or aldehyde to produce an alkene
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Ylide
Characterized by adjacent charged atoms that each have a complete octet of electrons
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If a carbon has a positive charge, can it be part of an ylide?
No because it does not have a complete octet
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Which step is responsible for the mixture of E and Z isomers in the Wittig reaction?
Step 1 (determines stereoselectivity)
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Soft nucleophiles are ____ have ____ addition and take place under ____ control
- Reversible
- Conjugated
- Thermodynamic
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Hard nucleophiles are ____ have ____ addition and take place under ____ control
- Irreversible
- Direct
- Kinetic
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What are the reaction conditions when using LiAlH4
- Needs an aprotic solvent
- Always requires a workup step
- Happens in two steps (stepwise)
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What are the reaction conditions when using NaBH4
- Needs a protic solvent
- Happens in one step (concerted)
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Reacting an imine with NaBH4 or LAH creates a ____
Secondary amine
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Reacting a nitrile with NaBH4 or LAH creates a _____
Primary amine
(This is because you need two equivalents of the reagent to turn the triple bond into a single bond)
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When does condensation occur in an aldol reaction?
When there is heat, or when there are conjugation of aromatic rings
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Hemiacetal
When an O and OH are bonded to the same carbon
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Why is hemiacetal formation sped up when there is slight acid or base present?
If the reaction is neutral, then there will have to be both protonation and deprotonation after nucleophilic attack. If there is base or acid present, then there will only have to be one step after nucleophilic attack
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When going from a fischer projection to a cyclic structure, the right side corresponds with ____ while left side is ____ for a D sugar
Also, the very last molecule at the end of the projection will be UP if it is a D sugar
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Mutarotation
When two anomers are present in the same solution
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Anomer
Another word for diastereomers
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In the alpha anomer of a monosaccharide the anomeric OH and OHCH2 are _____ to each other, while a beta anomer is ____
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How are hemi acetals formed?
When an aldehyde or ketone are treated with OH
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How are acetals formed?
When an aldehyde or ketone are treated with excess OH
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Acetal
When two O-R are bonded to the same carbon
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Why are acetals inert to strong bases and nucleophiles?
Because they cannot participate in resonance
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Why are diols used as protecting groups instead of OH?
Because with a diol there is entropic conservation. It is neutral, where adding an OH would make the system entropically unfavorable
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What are imines and how are they formed?
Imine has a C=N bond
Formed when C=O bond is treated with ammonia or primary amines in slightly acidic conditions
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What are enamines and how are they formed?
An amino group (N(CH3)2) attached to an alkene carbon
Formed when secondary amines are reacted with C=O
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What decides if a nucleophile is soft or hard?
The amount of charge it has.
Soft nucleophiles have a small charge while hard nucleophiles have a larger charge
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Wolf-Kishner reduction
Occurs when cyclopropylethanone is treated with hydrazine (NH2-NH2) results in two new C-H bonds
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When there is a diol, it will be making a _____ that makes an intramolecular ring
Protecting group
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____ and _____ amines form imines, while _____ form enamines under slightly acidic conditions
- Ammonia and primary amines
- Secondary amines
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In imine reactions, due to the very slight acidity, does protonation or nucleophilic attack happen first?
Nu- attack
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Crossed vs. Self aldol
A crossed aldol occurs when there are 2 different aldehydes or ketones
A self aldol occurs when the same aldehyde or ketone is present
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In the deprotonation of alpha carbons in aldol reactions, which product is the thermodynamic and which is the kinetic?
The thermodynamic product is the one made with an alkoxide at the more substituted carbon
The kinetic product is the one formed with LDA at the less substituted carbon
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What is the Robinson annulation?
The conjugate addition of an Enolate anion, followed by condensation
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What are the two considerations of the Robinson annulation?
One of the compounds must be an alpha/beta unsaturated carbonyl, and the other must be either a ketone or aldehyde
The alpha/beta unsaturated carbonyl must have two alpha hydrogens
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