Members that difere in number of methylene groups
What is the name for linear butane? For branched butane?
“n-butane” (n-denotes carbon on mother chain it’s attached to)
“iso-butane” b/c it’s a branched isomer
What is the IUPAC Rule regarding the Main Chain?
Find the longest continuous chain of C’s and use the name of this as the base of the compound (i.e. 6-C’s=”hexane”)
Use the chain with more substituents if there are 2 main chains of equal length
What is the IUPAC Rule for numbering the main chain?
Number main chain beginning with end nearest to a substituent
What is the IUPAC Rule regarding naming alkyl groups?
-Name substituent groups as alkyl groups, give location by number on main chain
-Replace “ane” on alkane with “yl”
What is the IUPAC Rule for organizing multiple groups?
When there are 2+ substituents, list in alphabetical order. When there are 2+ of the same, use prefixes.
Use longest alkyl as base, number with head carbon on main chain for complex subs.
What is the relationship for BP for alkanes?
As MW and SA increase, BP does as well.
Same relationship, but those with EVEN numbers of carbon pack tighter and require a higher MP. Also, BRANCHING INCREASES MP as they pack tighter.
Alkane Combustion general formula
Alkane Halogenation general formula
Alkane + O2 –> CO2 + H2O + Heat
Alkane + Halogen —> alkyl alides (CH2Cl2)
(usually requires light/heat)
Ethane general structure
Dihedral Angle (theta); eclipsed, staggered, skew
Theta with most PE?
2 CH3’s with overlapping sp3’s to form a sigma bond.
Angle between H-C bonds on front and back C.
-Eclipsed=0 deg.<–MOST PE from torsion
How does the torsional energy compare to ethane?
Higher, approximately 1.2 kJ.
Measuring theta in Butane
Totally eclipsed, gauche, anti
Between the two methyl groups
totally eclipsed= methyls pointed in same direction, 0 deg
gauche= 60 deg, methyls to L and R of ea other
anti= 180 deg, CH3 point opp directions
Lowest= anti, then gauche from separating CH3s
General molecular formula of cycloalkanes
How to number and name based on substituents
Identifying cis vs. trans isomerism
Number so that substituted Cs get lowest numbers, name in alphabetical order
cis= subs point to same face, trans= point to opp face
Angle (“Baeyer”) Strain
General bomb calorimeter RXN
C-C bonds don’t hae optimum overlap, so require angle other than 109.5 deg. and have eclipsed confs
(CH2)n + 3/2 O2 –> nCO2 + nH2O+ n(energy/CH2)
Find energy by dividing heat of combustion by n.
high ring strain to 60 deg bond angle, eclipsed torsional strain, planar geometry
slightly folded form w/ 88 deg bond angle
envelope conf that undulates with up/down motion of methylene grps
Does cyclohexane have ring strain?
Which confs are most stable? Highest energy?
NO RING STRAIN
Chair is most stable with all at 109.5 deg, boat stable but has torsional strain, twisted boat reduces eclipse of flagpole H’s.
Half chair has highest energy (rocket ship!)
Axial Bonds (odd/even)
Equitorial Bonds (odd/even)
Axial= H-C bond parallel to ring
-odd Cs have axial up
-even Cs have axial down
Equitorial= H-C bond point along ring equator
-odd Cs have equitorial down
-even Cs have equitorial up
For monosubstituted cyclohexanes in a ring flip, what’s the intermediate conf?
Axial/Equitorial–what’s the favorable methyl position?
1,3- Diaxial Interaction
equitorial, creates anti conformation
when methyls are smooshed near another H when in axial position
For disubstituted cyclohexanes, do we want cis confs with both axial or equitorial?
How about trans confs?
Position of large/small subs?
Fine, present in equal amounts but higher energy b/c of 1 axial sub.
Large should be equitorial, small axial if can’t have cis. Want tert-butyls in equitorial.
-x= largest c-bridge
z=smallest # c-bridge
For cis decalin (bicyclo[4.4.0]decane), what do you need? Trans decalin?
cis= need 1 bond to right ring axial, 1 equitorial
trans=both bonds to right ring need to be equitorial, rigid conf