Chapter 2

Question 1

branched hydrocarbons with multiple substituents

Answer 1

• if same substituent appears twice, use prefixs “di”, “tri”, etc
  1a. ) if same quantity of two or more substituents occurs, then assign the lowest number to the first alphabetical substituent
  1b. ) if different quantities of two or more subsitutents occurs, then assign the lowest number to the carbon containing the greatest number of substituents

Question 2

branched hydrocarbons with complex side-chains

Answer 2

• complex substituent names included in parentheses after number indicating location
• for complex molecules with two or more posible parent chains, choose the one with the greatest number oif substituents
• begin numbering the complex subsituent at its point of attachment to the parent chain (ie, first carbon away froim the parent chain takes 1)

Question 3

isopropyl

Answer 3

R-< (three carbon unit)

Question 4

characteristics of “isoalykl” vs “sec-alkyl” and “tert-alkyl” compounds

Answer 4

• isoalkyl, sec-alkyl, and tert-alkyl occur at the end of the chain
• “iso” not hyphenated; “sec-alkyl” and “tert-alkyl” hyphenated
• “iso” counts towards alphabetization; neither “sec-alkyl” mor “tert-alkyl” count towards alphabetization

Question 5

classification of carbons and hydrogens in a system

Answer 5

• type of carbon and hydrogen based on the number of other carbons attached to the carbon, or the carbon to which the hydrogens are bonded
• primary (1^o): carbon bonded to one other carbon; hydrogens bonded to carbon bonded to only one other carbon
• secondary (2^o): carbon bonded to two other carbons; hydrogens bonded to carbon bonded to two other carbons
• tertiary (3^o): carbon bonded to three other carbons; hydrogen bonded to carbon bonded to three other carbons
• quaternary (4^o): carhbon bonded to four other carbons; no such thing as a quarternary hydrogen

Question 6

naming cycloalkanes

Answer 6

• add “cyclo” to front of parent alkane
  1. ) no number necessary for cycloalkane with only one substituent (carbon with substituent understood as first carbon)
  2. ) named alphabetically, with lowest number attached to the first substituent which appears alphabetically
  3. ) for two or more subsitutents, naming occurs to minimize the number combination and only in one direction

Question 7

formula of cycloalkanes

Answer 7

C_nH_2n

Question 8

constitutional isomers

Answer 8

same formula, but different skeleton

Question 9

how to determine isomers

Answer 9

1. ) draw straight chain
2. ) systematically move groups (methyls, alcohols, etc)
3. ) check for redundancy

Question 10

allkane confirmations

Answer 10

3D arrangements of atoms in a molecules that result from sigma-bond rotation

Question 11

dihedral angle

Answer 11

angle between planes formed by carbons and hydrogens (or other substituent groups)

• can be visualized like an onpen book

Question 12

staggered confirmation

Answer 12

lowest energy confirmation; occurs when hydorgens or substituents farthest away from one antoher as possible

Question 13

between what types of molecules do gauche interactions occur?

Answer 13

gauche interactions occur between non-hydrgoen molecules (eg alkyl groups, halides, etc)

Question 14

gauche confirmation

Answer 14

methyl groups for a C_n>3 alkane on neighboring carbons have bond angle of 60º; not as high in energy as eclipsed confirmation but still not as low in energy as the staggered confirmation

• occur only on non-hydrogen groups; therefore does NOT occur for ethane

Question 15

how much energy does a gauche confirmation “cost” from the staggered confirmation?

Answer 15

0.9 kcals / mol

Question 16

eclipsed confirmation

Answer 16

dihedral angle = 0; confirmation of greatest energy (methyl groups and/or hydrogens aligned with one another)

Question 17

anticonfirmation

Answer 17

dihedral angle of ~120° on molecule of butane;

Question 18

types of strain

Answer 18

1. ) tortional strain - occurs from eclipsing interactions
2. ) steric strain - groups on neighboring carbons “bump into” one another
3. ) angle strain - bond angles on molecule in reality not equivalent to theoretical bond angles based on molecular geometry

Question 19

how do molecules attempt to handle total strain?

Answer 19

molecules adapt by accepting some of each type of strain

• analogy: in order to sleep somewhere uncomfortable, one contorts in several places until acceptable. same with molecules and strain.

Question 20

diaxial interactions

Answer 20

parallel axial substituents create steric strain

Question 21

for every axial substituent on cyclohexane, how many gauche interactions with the ring are created?

Answer 21

two

Question 22

for neighboring carbons with substituents, under what circumstances are gauche interactions created?

Answer 22

gauche interactions will occur in every circumstance other than when the two substituents are in anti-confirmation from one another (ie, one points north and the other south)