Class 1 Flashcards
When is a molecule unsaturated?
When there is at least 1 pi bond or ring
1 pi bond = 1 degree of saturation
2 pi bonds = 2 degrees, etc.
How do you calculate degree of unsaturation?
DOU = (2n + 2 - x)/2
n= number of carbons x= number of hydrogens
- Treat halogens like hydrogens
- Ignore oxygens
- Subtract the number of Nitrogens from x and then apply
What are properties of unstable molecules
High in energy
Reactive with environment
Shorter lifetimes
What are properties of stable molecules
Low in energy
Less reactive with environment
Longer lifetimes
What is the ideal bond angle?
109.5 degrees, smaller than that = ring strain
What is the typical donating group/subsitituent?
Alkyl group
As such, alkyl R groups will push electrons away and thus stabilize a cation and destabilize an anion.
What are typical withdrawing (EN) groups?
O, N, halogens
What are three principles about resonance structures?
- Generally, more resonance structures = greater stabilization
- Delocalization can only occur through ADJACENT p orbitals!
- Lowest energy (most stable) resonance structures contribute most to hybrid
What three factors indicate the best resonance structure?
- The octet rule satisfied for ALL atoms!!!!!!!!
- The least formal charge
- Neg charge on more EN atoms
What is the most stable type of cation?
Tertiary!
What is required to have resonance structures?
A pi bond!
What defines a Bronsted-Lowry acid?
Wants to donate a H+ and leave behind a conjugate base.
What 3 factors affect acid strength and how?
By stabilizing the conjugate base:
- Electronegativity -> more EN atoms handle negative charge better.
- Resonance structure for anion conjugate base
- Induction
What is a Lewis base?
Nucleophile (negatively charged an/or lone pair of e- to donate)
Think LEWis NUcleophile
Nucleophiles are Lewis ________.
Bases
What are some nucleophilic trends?
When comparing the same atom, a negative charge makes a stronger nucleophile
For atoms in the same row, nucleophilicity increases as electronegativity DECREASES
For atoms in the same column, nucleophilicity increases as size increases (down the periodic table)
Electrophiles are typically electron ______.
Deficient
Electrophiles are Lewis ______
Acids
What are abbreviations of some good leaving groups? What makes them good LGs?
Tosylate (TsO-)
Mesylate (MSO-)
Acetate (ACO-)
Good LGs because they have lots of resonance
What makes something a good LG?
- Resonance
2. Weak base (e.g. Cl-
What is another name for a structural isomer?
Constitutional
What is a structural (constitutional) isomer?
Same molecular formula, but different connectivity
What is a conformational isomer?
Differ by rotation about a sigma bond (but same molecular formula and connectivity…because of this they have the same chemical and physical properties).
Cannot be isolated
In a Newman projection, equal spacing of group is called what?
Staggered conformation
In a Newman projection, unequal spacing (“covering” of each other) of groups is called what?
Eclipsed conformation
What is the difference between anti, gauche, and syn conformation?
Anti = 90 deg apart Syn = right on top of each other Gauche = in between
Is axial or equatorial positioning more stable for bulky groups?
Equatorial
What is chirality?
A molecule with no plane of symmetry, its mirror image is not superimposable.
What makes something a chiral center?
- Sp3 hybridized
- All bonds must be to different substituents
- Tetrahedral geometry
Is a chiral center a stereocenter?
Yes
What is another name for clockwise rotation?
Dextrotatory
What is another name for counter-clockwise rotation?
Levorotatory
What is the key rule about assigning R-S configurations?
Atoms with the highest atomic number take priority
Clockwise = an ________ configuration.
R
Counter-clockwise = an ________ configuration.
S
What is a stereoisomer?
Same atomic connectivity
Different spatial arrangement of substituents – usually around chiral centers
e.g. enantiomer
What is an enantiomer?
Non-superimposable mirror images
Each enantiomer has the opposite configuration at ALL chiral centers
Each enantiomer has optical rotation of equal magnitude, but opposite sign
They have identical chemical and physical properties!! (but are optically different, opposite of each other in fact).
What is a racemic mixture? Is it optically active?
50:50 mix of enantiomers
Will not be optically active?
What is resolution?
The process of separating enantiomers
What are diastereomers?
Nonsuperimposable, NON MIRROR IMAGES
Opposite configuration for at least one, BUT NOT ALL chiral centers
Different chemical and physical properties…can be separated! Obviously different optically as well.
What is a geometric isomer?
A subset of diastereomers
Restricted in rotation about a double bond or ring
Does not require chiral centers
ALL chemical and physical properties are different
e.g. E vs Z
Cis configuration is equivalent to ____ configuration.
Z
think Zame (same) side
Trans configuration is equivalent to ____ configuration.
E
They’re on the Epposite (opposite) side
Generally trans is more stable than cis, but not always
What is an epimer?
Subset of diastereomers that differ in configuration at ONLY ONE chiral center
What is required for a compound to be mesoi
Must contain an even number of chiral centers
Must contain an internal plane of symmetry
Symmetrical chiral centers MUST have opposite configurations, thus are not optically active! Kinda like gluing R and S together
What types of substituents will increase acidity of a compound?
EWG groups (e.g. N, O, etc.)
When naming compounds do you list substituents alphabetically?
Yes!
