Term
Major Functional Groups and Nomenclature |
|
Definition
- Nomenclature
- identify the longest carbon chain containing the highest-order functional group
- number the chain
- name the substituents
- assign a number to each substituent
- Naming substituents and functional groups
[image]
[image] |
|
|
Term
Structural(Constitutional) Isomers |
|
Definition
- isomers of this type are the least similar of isomers
- only share molecular formula and weight
- don't share connectivity
- vary in physical and chemical properties
[image] |
|
|
Term
Conformational Isomers and types of confirmations |
|
Definition
- subdivision of stereoisomers
- share same connectivity, but differ in how these atoms are arranged in space
- conformational are most similar of all isomers and are in fact the same molecule aside from natural rotation about single (σ) bonds
- described best using newman projections which show angles of atoms and groups in relevance to each other
- best thought of in terms of straight-chain and cyclic conformations
- straight-chain: staggered/anti, gauche, (totally) eclipsed
- cyclic: referred to be conformational shapes; chair, envelope, boat, puckered, etc.
[image] |
|
|
Term
Straight-Chain Conformations |
|
Definition
- way of thinking about conformational isomers as applied to straight chains (as opposed to cyclic molecules)
- looks at angles separating different atoms/functional groups from one another
- staggered - no overlap of atoms along line of sight
- anti - particular type of staggered conformation in which largest functional groups are 180° from one another; most stable
- gauche - particular type of staggered conformation in which largest functional groups are w/in 60° of one another; less stable
- eclipsed - conformation in which groups or atoms are overlapping
- eclipsed - largest groups are 120° apart (but are overlapping w/ other groups/atoms)
- totally eclipsed - largest groups are 0° apart (totally overlapping); least stable
[image]
- conformational interconversion barriers are small and easily overcome at room temperature
|
|
|
Term
Cyclic Conformations and Cyclohexane |
|
Definition
- way of thinking about conformational isomers as applied to cyclic molecules (as opposed to straight-chain)
- described by particular terms relating to overall shape
- stability of conformation is based on ring strain(based on three types of strain)
- angle strain - when bond angles deviate from ideal values through compression or stretching
- torsional strain - when cyclic molecules must assume conformations that have eclipsed or gauche interactions
- non-bonded strain (van der Waals repulsion) - non-adjacent atoms or groups compete for same space
- cycloalkanes attempt to adopt non-planar conformations to alleviate strain
- cyclohexane's most stable form is known as the chair conformation
- atoms surrounding main ring are referred to by their orientation with the plane of the ring
- axial groups/atoms are perpendicular to plane of ring and stick up or down
- equatorial groups/atoms are parallel to plane of ring and stick out
- bulkiest groups surrounding cyclohexane favor the equatorial position to reduce flagpole interactions arising from van der waals repulsion
- chair flip - when cyclohexane goes from one chair form to another
- must pass through half-chair conformation (high energy)
- at end of flip, all axial groups become equatorial and vice versa
[image] |
|
|
Term
|
Definition
- subdivision of stereoisomers (other being conformational)
- these isomers are less similar as they must undergo a break and reformation in covalent bonds to change from one form to another
- determined based on their ability to be superimposed over one another and whether or not they are mirror images
- enantiomers - non-superimposable mirror images
- diastereomers - non-superimposable isomers that are not mirror images
[image] |
|
|
Term
|
Definition
- optical isomers are molecules in which spatial arrangement of groups affects the rotation of plane-polarized light passing through
- rely on chirality
- if mirror image of molecule/center cannot be superimposed on original molecule, then it is chiral
- only chiral molecules can be considered optically active
- mixtures of chiral molecules of opposite types (enantiomers) in equal ratios create optically inactive mixture termed racemic
- (+) - compound that rotates plane of polarized light to right - dextrorotatory (d-)
- (-) - compound that rotates plane of polarized light to left - levorotatory (l-)
- can only be determined experimentally and not by looking at the molecule's structure
|
|
|
Term
|
Definition
- subset of configurational isomers that are nonsuperimposable mirror images of one another
- must have opposite configurations at every chiral center
- have identical chemical and physical properties
- only differ in optical activity and reactions in chiral environments
- optical activity
- reactions in chiral environments
- if racemic mixture reacted w/ (+), (+,+) and (-,+) are formed
- if racemic mixture reacted w/ (-), (-,-) and (+,-) are formed
[image] |
|
|
Term
|
Definition
- subset of configurational isomers that are non-superimposable and non-mirror images of each other
- can only occur if molecule has two or more chiral centers
- for any molecule w/ n chiral centers, 2n possible diastereomers(and stereoisomers) exist
- have different chemical and physical properties
- can behave in chemically similar ways due to presence of same functional groups
- consistently different in physical properties due to differing spatial arrangements
- diastereomers are optically active, but knowing the way that one diastereomer rotates polarized light, gives no indication as to how another might
- by pulling individual enantiomers from pairs and comparing them to enantiomers from other pairs, we can identify diastereomers
- I and II are not diastereomers of one another, but I and III or I and IV are
[image] |
|
|
Term
|
Definition
- a molecule containing one or more chiral centers that is not optically active due to the presence of an internal plane of symmetry
- molecular equivalents of racemic mixtures - chiral centers cancel out
[image] |
|
|
Term
Relative Configuration vs. Absolute Confirmation of Stereoisomers |
|
Definition
- configuration of stereoisomer - spatial arrangement of atoms or groups in molecules
- relative configuration - configuration of chiral molecule in relation to another chiral molecule
- often through chemical conversion
- used to determine whether molecules are enantiomers, diastereomers or same molecule
- require comparison of molecules
- absolute confirmation - describes exact spatial arrangement of atoms or groups independent of other molecules
- can be described using E/Z, cis/trans, and R/S
|
|
|
Term
|
Definition
- Cis/Trans system
- used to describe geometric isomers that are a particular types of diastereomers
- substituents must differ in position around immovable bond
- really only applies to double bonds or cyclic molecules w/ one substituent on each side of the bond
- indicates different molecules that cannot interconvert w/out breaking of a pi bond
- cis - same side
- trans - opposite sides
[image]
- E/Z system
- similarly used to describe geometric isomers, but can include molecules w/ more than one substituent on either side of the immovable bond
- E (entgegen or opposite) - two highest-priority substituents are on opposite sides of bond
- Z (zusammen or together) - two highest-priority substituents on same side of bond
[image] |
|
|
Term
|
Definition
- used for chiral centers in molecules
- R (rectus - right) and S (sinister - left)
- To determine
- assign priority to groups surrounding center
- arrange molecule in space with lowest priority group facing back
- connect 1→2, 2→3, and 3→1 using arrows to create circle
- determine directionality of circle (clockwise or counterclockwise)
- Clockwise means that center must receive R designation
- Counterclockwise means that center must receive S designation
- Name molecule by putting (R) and (S) in parentheses and separating from rest of name by hyphen
|
|
|
Term
|
Definition
- formed when two atomic orbitals combined
- obtained mathematically by adding or subtracting the wave functions of the atomic orbitals
- if signs of wave functions are same, lower-energy bonding orbital produced
- if signs of wave functions are opposite, high-energy antibonding orbital produced
[image]
- when formed by head-to-head or tail-to-tail overlap, resulting bond is called σ bond (single bond)
- when two p-orbitals line up in parallel, their electron clouds can overlap to form π bond
- are extremely weak bonds(in comparison to σ) and don't form unless σ bond is present
- 1 π bond w/ a σ creates double bond
- 2 π bonds w/ a σ create triple bond
[image] |
|
|
Term
Theory of Orbital Hybridization |
|
Definition
- accounts for why a molecules like methane which takes 2 electrons from 2s orbital, one from the px-orbital, and one from the py-orbital (different energies) still forms 4 equivalent bonds
- these orbitals are formed by mixing different types of orbitals to produce a new orbital with hybrid s and p character
- sp3
- tetrahedral geometry
- no unhybridized p-orbitals to form π bonds
- accomplished by promoting one 2s electron into 2pz-orbital to produce four valence orbitals containing one electron each
- 25% s character and 75% p character
[image]
- sp2
- trigonal planar geometry
- one unhybridized p-orbital can be used to form one π bond
- one s-orbital is mixed w/ two p-orbitals and 3 sp2 orbitals are formed
- bonds are 120° apart
- 33% s and 67% p character
- sp
- linear geometry
- two unhybridized p-orbitals can be used to form two π bonds
- one s-orbital is mixed w/ one p-orbital to form two sp orbitaals
- 50% s and 50% p character
- oriented 180° apart
- can be triple bond or two single bonds
|
|
|
Term
|
Definition
- delocalization of electrons that occurs in molecules w/ conjugated bonds
- imparts increased stability
- can also give a bond partial double-bond character like in proteins (making it immovable)
- conjugation - alternating single and double/triple bonds
- allows for alignment of a number of unhybridized p-orbitals along backbone of molecule
- π electrons can delocalize throughout this p-orbital system
- actual structures of molecules with resonance forms is something between all possible resonance forms
- some forms are favored based on stability giving molecules more character of one form
- lack of formal charges
- formation of full octets on highly electronegative atoms (O or N)
- stabilization of + and - charges through induction and aromaticity
|
|
|