Ch2 Flashcards
Alkanes and cycloalkanes are
Saturated Hydrocarbons that only have single bonds
Alkanes and cycloalkanes are ___ - hybridized with what degree?
Sp^3 and 109.5
What is the first step in naming alkanes?
Finding the longest parent chain
When naming alkanes, what does the prefix indicate and what are the first 10?
# of carbons Meth-1 Eth-2 Prop-3 But-4 Pent-5 Hex-6 Hept-7 Oct-8 Non-9 Dec-10
Where are substituents located?
They branch from the parent chain
When numbering alkanes, where should you start?
At the end closest to a substituent to give it the lowest possible number
If there are mutltiple substituents what should you do?
Number the parent to give lowest numer to substituent closest to an end then list substituents in alphabetical order
If there are identical subsitituents
The prefix di, tri, and tetra are not considered in alphabetizing
Memorize isopropyl, isobutyl, sec-butyl, tert-butyl, amd neopentyl
**when alphabetizing, ignore hyphenated prefixes sec- and ter-
Assume C is binded to _ unless anither substituent is labeled
H
1 C is bonded to how many C’s an H’s?
2 C?
3 C?
4 C?
1 carbon and 3 primary H’s
2 Cs and 2 secondary Hs
3 Cs and 1 tertiary H
4 Cs and no Hs
How does the nomenclature for cycloalkane work?
Put cyclo before alkane root
If 2 substituents, #1 goes to group that comes first alphabetically
What are bicycloalkanes?
Alkanes with two rings that have carbons in common
What are bridgehead carbons
The carbon atoms shared by all two-ring sets
In bicycloalkanes, the # of carbons in the parent are the two bridgehead carbons plus
All of the bridging carbons
Bridge lengths go in ____ in ____ order
Brackets []
Descending
Given a choice, give lower numbers to___ or ____
Functional groups or substituents
General IUPAC rules
Parent: prefix-infix-suffix
Prefix: # of C atoms
Infix: type of C-C [an: C-C bonds; en: ≥1 C=C bond; yn: ≥1 C triple bond C
Suffix: functional group
Suffix functional groups
- e: hydrocarbon (R-H)
- ol: alcohol (R-OH)
- al: aldehyde (R-CH=O)
- amine: amine (RR’R”N)
- one: ketone (R-C(=O)-R’)
- oic acid: carboxylic acid (R-C(=O)-OH)
Eclipsed ethane is _ energy / _ stable than staggered ethane because of
Higher
Less
Torsional strain
Torisonsl strain is also known as and is?
Bonded strain
The energetic cost of the repulsion of the electrons in eclipsed bonds
In butane, the methyl groups move _ each other as you rotate 60°
Away
If not anti, it must be
Gauche
Non-bonded strain=
Steric strain
What is strain?
The increase in the pe of a molecule due to the deviation in its structure from ideal values
Components of strain in molecules
Angle strain Torsional strain Non-bonded strain Bond strain Coulumbic strain
Angle strain
Compression or expansion of a bond angle
Torsional strain
When bonds are not staggered
Non-bonded strain
When two remote groups approach too closely (usually destabilizing, sometimes stabilized); ex:gauche
Bond strain
Compression or stretching of bonds
Coulumbic strain
Stabilizing or destabilizing
Cyclopropane has 28 kcal/mol of strain due to
Angle strain: the C-C-C bond angles are compressed from 109.5° to 60°
Torsional strain: there are 6 sets of eclipsed hydrogen interactions with H-C-C-H = 0°
Cyclobutane has _ kcal/mol of strain
Cyclopentane has _ kcal/mol of strain
26
6.5
Planar cyclobutane and cyclopentane try to reduce _ strain but this increases _ strain (a trade-off)
Torsional
Angle
In cyclobutane, the best compromise has C-C-C = ___ and H-C-C-H = ___
88°
24°
The two chair conformations in cyclohexane
Have no angle or torsional strain
- C-C-C Angles are ideal: 109.5°
- all bonds are staggered
Boat conformation for cyclohexane
6.5 kcal/mol strain vs. chair conformer
Nonbonded strain due to flagpole interactions
Eclipsed across two C-C bonds
Twist-boat conformation for cyclohexane
5.5 kcal/mol strain vs. chair conformation
Nonbonded strain is greatly reduced vs. boat
Some torsion strain from partially eclipsed C-H bonds
How many gauche interactions does the axial methyl group have in Methylcyclohexane? What about the equatorial conformation?
Axial methyl has gauche interactions and equatorial conformation has no gauche interactions
Cis-isomers:
Trans-isomers:
Cis- both groups are on same side of ring
Trans- groups are on opposite sides of the ring
Cis- trans isomers are ___ isomers; possible in ___ and ___; and have the same ___ and ___ but are ___
Geometrical
Rings and alkenes
Molecular formula and atom connectivity
Not interconverted via rotation about single bonds
Bp of methane, butane, pentane, decane?
Methane = - 164°c
Butane = 0°c
Pentane = 36°c
Decane =174°c
Intermolecular attractive forces…. Ion/ion = Dipole/dipole= H-bonds = Ion/dipole =
Very strong
Very weak
Moderate
Strong
London dispersion forces are ____ that depend on
Instantaneous dipole/induced dipole
The total contact surface area between molecules
Two limiting cases when comparing two molecules (London dispersion forces)
If the shapes are the same, then the forces increase as the number of atoms increases
If the number of carbons is the same, then the forces decrease with increased branching
Chrial centers have to have __ different substituents
4
Objects that are not superimposable on their mirror images are __ and show handedness… they are different.
Chiral
Objects that are superimposable on their mirror images are ___ and do not show handedness. An ___ object has at least one element of symmetry. They are the same
Achiral
Plane of symmetry (mirror plane) is an
Imaginary plane through an object where one half is the mirror image of the other half
Center of symmetry at the atom (x,y,z) is
The exact same as the atom at (-x,-y,-z) for all atoms in the molecule (inversion center)
A tetrahedral atom bonded to four different groups is
A chiral (asymmetric) center
A stereocenter is an atom where
The interchange of two groups gives a atereoisomer of the original molecule
A carbon bonded to H, CH3, I and Cl is
A chiral center amd stereocenter
All chiral centers are
Stereocenters but all stereocenters are not chiral
When it comes to R and S, the higher the atomic number, the ….. and if it cannot be assigned using the atoms bonded to the chiral center, use
Higher the priority… the next set of atoms
When naming enantiomers…
- ) locate the chiral center
- ) prioritize each substituent from 1-4
- ) draw an arc from 1-3
- ) CW= R, CCW= S
- ) but if lowest priority isn’t on dash, switch R or S
How do you figure out how many stereoisomers a molecule has?
2^(# of chiral centers)
With meso compounds, the mirror place is ____; therefore
The exact same; not an enantiomer
What are Meso compounds and what must they have?
An achiral compound possessing two or more chiral centers that must have an internal mirror plane of symmetry or an inversion center
Enantiomers have ___ physical and chemical properties while diastereomers have ____ physical and chemical properties
Identical
Different
Enantioners become ___ in a chiral environment
Diastereomeric
In Fischer projections, vertical bonds ____ while horizontal bonds ____
Vertical: bonds projecting away from you
Horizontal: bonds projecting toward you
There is angle strain whenever
An angle is less than 109.5 degrees
Gauche interactions occur
Whenever 2 non-hydrogen molecules are 60 degrees away from each other
