WWU Chem 351 Chpt 3

Flashcard maker : Robert Carter

Methylene Group










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? 


For MP?

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)

Methane bond angle

PERFECT 109.5 degrees.

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

-Staggered=60 deg.

-Skew=any theta




How does the torsional energy compare to ethane?



Higher, approximately 1.2 kJ.

Measuring theta in Butane


Totally eclipsed, gauche, anti


Lowest energy?

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?



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

boat conformation


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.

Naming bicyclic alkanes


-x= largest c-bridge

y=mid 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

Get instant access to
all materials

Become a Member