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WWU Chem 351 Chpt 3

question

Methylene Group

 

 

 

Homologs

answer

-CH2-

 

 

 

 

Members that difere in number of methylene groups

question

Butane

 

What is the name for linear butane?  For branched butane?

answer

C4H10

 

“n-butane” (n-denotes carbon on mother chain it’s attached to)

;

“iso-butane” b/c it’s a branched isomer

question

What is the IUPAC Rule regarding the Main Chain?

answer

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

question

What is the IUPAC Rule for numbering the main chain?

answer

Number main chain beginning with end nearest to a substituent

question

What is the IUPAC Rule regarding naming alkyl groups?

answer

-Name substituent groups as alkyl groups, give location by number on main chain

-Replace “ane” on alkane with “yl”

question

What is the IUPAC Rule for organizing multiple groups?

answer

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.

question

What is the relationship for BP for alkanes? 

 

For MP?

answer

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.

question

Alkane Combustion general formula

 

 

Alkane Halogenation general formula

answer

Alkane + O2 –> CO2 + H2O + Heat

 

 

Alkane + Halogen —> alkyl alides (CH2Cl2)

(usually requires light/heat)

question

Methane bond angle

answer

PERFECT 109.5 degrees.

question

Ethane general structure

 

Dihedral Angle (theta); eclipsed, staggered, skew

 

Theta with most PE?

answer

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

 

question

Propane

 

How does the torsional energy compare to ethane?

answer

C3H8

 

Higher, approximately 1.2 kJ.

question

Measuring theta in Butane

 

Totally eclipsed, gauche, anti

 

Lowest energy?

answer

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

question

General molecular formula of cycloalkanes

 

How to number and name based on substituents

 

Identifying cis vs. trans isomerism

answer

CnH2n

 

Number so that substituted Cs get lowest numbers, name in alphabetical order

 

cis= subs point to same face, trans= point to opp face

question

Angle (“Baeyer”) Strain

 

General bomb calorimeter RXN

answer

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.

question

Cyclopropane

 

Cyclobutane

 

Cyclopentane

answer

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

question

Does cyclohexane have ring strain?

 

Which confs are most stable?  Highest energy?

answer

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!)

question

Axial Bonds (odd/even)

 

Equitorial Bonds (odd/even)

answer

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

question

For monosubstituted cyclohexanes in a ring flip, what’s the intermediate conf?

 

Axial/Equitorial–what’s the favorable methyl position?

 

1,3- Diaxial Interaction

answer

boat conformation

 

equitorial, creates anti conformation

 

when methyls are smooshed near another H when in axial position

question

For disubstituted cyclohexanes, do we want cis confs with both axial or equitorial?

 

How about trans confs?

 

Position of large/small subs?

answer

EQUITORIAL

 

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.

question

Naming bicyclic alkanes

answer

“bicyclo[x.y.z]prefix’tane'”

-x= largest c-bridge

y=mid c-bridge

z=smallest # c-bridge

question

For cis decalin (bicyclo[4.4.0]decane), what do you need?  Trans decalin?

answer

cis= need 1 bond to right ring axial, 1 equitorial

 

trans=both bonds to right ring need to be equitorial, rigid conf