Chapter 2 Flashcards
conformations: different … of atoms that result from … about a single bond
spatial arrangements; rotation
staggered conformation: atoms/ groups on adjacent carbons are as
far apart as possible
eclipsed conformation: atoms/groups on adjacent carbons are as
close as possible
compounds reside in … conformational state
lowest E
eclipsed conformation is less stable because of
hyperconjugation
in staggered conformation, highest molecular orbital overlaps with
smallest antibonding molecular orbitals
… conformation: all conformations between staggered and eclipsed
skew
anti conformation is when the groups are … apart
180 degrees
gauche: groups are
60 degrees apart
torsional strain: resistance to …, non-bonded atoms separated by 3 bonds forced from … to …
rotation; staggered; eclipsed
angle strain: bond angle is …/… compared to optimum values
expanded; compressed
steric strain: non-bonded atoms separated by 4+ bonds are
forced closer to each other
strain: a measure of the energy stored in a compound due to a
structural distortion
dihedral angle: the angle created by two …, each defined by … atoms
intersecting planes; three
the energy difference between the conformational extremes arise from the stabilization of the staggered conformation. This arises because of a small … interactinon between a filled C-H bonding MO of one carbon and the empty/unfilled C-H antibonding MO on the adjacent carbon with which it is aligned
donor-acceptor
puckering of the ring alters the strain energy in two ways:
(1) it decreases the … associated with eclipsed interactions but
(2) it increases further the … caused by the compression of C–C–C bond angles
torsional strain; angle strain
a boat conformation is considerably less stable than a chair because of th e… associated with four pairs of eclipsed C-H interactions and the … between the two “flagpole” hydrogens
torsional strain; steric strain
some of the strain in the boat conformation can be relieved by a slight twisting of the ring to a … conformation
twist-boat
as the size of the alkyl substituent increases, the preference for conformations with the group … increases
equatorial
alkanes are … hydrocarbons, containing only C-C …
saturated; single bonds
alkanes are … hydrocarbons because the physical properties of the higher members of this class resemble those of the long C-chain molecules we find in … and …
aliphatic; animal fats; plant oils
a hydrocarbon that contains one or more C-C double bonds, triple bonds, or benzene rings, is classified as an … hydrocarbon
unsaturated
alkane names (based on number of C): C: C2: C3: C4: C5: C6: C7: C8: C9: C10: C11: C12: C13: C14: C15: C16: C17: C18: C19: C20:
methane; ethane; propane; butane; pentane; hexane; heptane; octane; nonane; decane; undecane; dodecane; tridecane; tetradecane; pentadecane; hexadecane; heptadecane; octadecane; nonadecane; eicosane
alkanes have the general molecular formula
CnH2n+2
constitutional isomers are compounds that have the same … but different …
molecular formula; structural formulas
by “different structural formulas” we mean that constitutional isomers differ in the kinds of … they have (.., ..,. or …) and/or in the … of their atoms
bonds; single; double; triple; connectivity
to determine whether two or more structural formulas represent constitutional isomers, write the … of each and then compare them. all compounds that have the same molecular formula but different … are constitutional isomers
molecular formula; connectivities
The IUPAC name of an alkane with an unbranched chain of carbon atoms consists of two parts: (1) a … that indicates the number of .. atoms in the chain and (2) the … -ane to show that the compound is a …
prefix; carbon; suffix; saturated hydrocarbon
The IUPAC name of an alkane with a branched chain consists of a … that indicates the longest chain of C atoms in the compound and … names that indicate the groups bonded to the parent chain
parent name; substitutent
a substituent group derived from an alkane by the removal of a hydrogen atom is called an …; it is commonly represented by the symbol …
alkyl group; R–
We name alkyl groups by dropping the -ane from the name of the parent alkane and adding the suffix …
-yl
(Rules of IUPAC system) the name for an alkane with an unbranched chain of C atoms consists of a prefix showing the number of … in the chain and the ending ..
C atoms; -ane
(Rules of IUPAC system) for branched-chain alkanes, select the longest chain of C atoms as the … chain; its name becomes the root name
parent
(Rules of IUPAC system) Give each substituent on the parent chain a name and a number. the number shows the … of the … to which the substituent is bonded. use a hyphen to connect the number to the name
carbon atom; parent chain
(Rules of IUPAC system) if there is one substituent, number the parent chain from the end that gives the substituent the
lower number
(Rules of IUPAC system) if there are two or more identical substituents, number the parent chain from the end that gives the lower number to the substituent … The number of times the substituent occurs is indicated by a … A … is used to separate position numbers
encountered first; prefix (e.g. di, tri); comma
(Rules of IUPAC system) if there are two or more different substituents, list them in … and number the chain from the end that gives the lower number to the substituent … if there are different substituents in equivalent positions on opposite ends of the parent chain, give the substituent of lower … the lower number
alphabetical order; encountered first; alphabetical order
the prefixes di-, tri-, tetra-, and so on, are … in alphabetizing. Alphabetize the names of the substituents first and then insert prefixes
not included
where there are two or more parent chains of identical length, choose the parent chain with the
greater number of substituents
the fact that an alkane chain is unbranched is sometimes indicated by the prefix … (…)
n-; normal
for branched chain alkanes beyond propane, … indicates that one end of an otherwise unbranched chain terminates in a … group, and … indicates that it terminates in -C(CH3)3
iso; (CH3)2CH; neo
the name we give to any compound with a chain of carbon atoms consists of three parts: a …, an … and a …
prefix; infix; suffix
the prefix indicates the number of carbon atoms in the parent chain; the infix indicates the … of the C-C bonds in the parent chain (whether they are …, …, or …)
nature; single; double; triple
infixes:
- an: … bonds
- en: one or more … bonds
- yn: one or more …
single; double; triple
the suffix indicates the class of compound to which the substance belongs:
- e: …
- ol: …
- al: …
- amine: …
- one: …
- oic acid: …
hydrocarbon; alcohol; aldehyde; amine; ketone; carboxylic acid
cycloalkanes contain … fewer hydrogen atoms than an alkane with the same number of C atoms and have the general formula ..
two; CnH2n
to name a cycloalkane, prefix the name of the corresponding open-chain alkane with … and name each substituent on the ring. if there is only one substituent on the cycloalkane ring, there is no need to …
cyclo-; give it a number
if there are two substituents, number the ring by beginning with the substituent of lower … If there are three or more substituents, number the ring to give the substituents the lower set of … and list them in …
alphabetical order; numbers; alphabetical order
an alkane that contains two rings that share two C atoms is classified as a … The shared C atoms are called … Cs, and the carbon chain connecting them is called a
bicycloalkane; bridgehead; bridge
the general formula of a bicycloalkane is …
CnH2n-2
difference between torsional and steric strain:
torsional is repulsion on … c atoms, when they are …
steric is when repulsion occurs between C/groups that are not … (e.g. … interactions)
neighboring; eclipsing; neighboring; diaxial
the interconversion between the strained and relaxed structures results from … and .. motions
collisions; thermal
in a newman projection, a molecule is viewed down the axis of a .. bond. the three lines in front represent bonds directed … you, whereas the three lines in back …
C-C; toward; point away from you
different conformations are often called … or …
conformational isomers; conformers
the lowest E (most stable) conformation is a … conformation; the highest energy (least stable) is an .. conformation
staggered; eclipsed
torsional strain arises when nonbonded atoms achieve conformations via rotations around bonds where they are closer to one another than in a more stable
alternate conformation
the two gauche conformations have equal … and are related by …
energies; reflection
small ring strain: exists in ring sizes below .. carbons and is due to the C-C-C bond angles not being able to achieve the optimal …
six; tetrahedral angle
nonplanar/puckered conformations are favored in all cycloalkanes larger than
cyclopropane
In cyclopentane, the ring will form a … conformation, where four C are in a plane and the 5 bends out. This is an energetic compromise that balances a decreased … strain with an increased … strain
envelope; torsional; angle
diaxial interaction is a kind of … strain that refers to the strain between an axial … and an axial … (or another group) on the same side of a cyclohexane group
steric; substituent; hydrogen
the preference for the equatorial position among the halogens increases in the order … < …. < … < ..
F; I; Cl; Br
stereoisomers are compounds that have (1) the same …
(2) the same … of their atoms
(b) but a different … of their atoms in space
molecular formula; connectivity; orientation
cycloalkanes with substituents on two or more carbons of the ring show a type of stereoisomerism called …
cis, trans isomerism
the prefix cis indicates that the substituents are on the … side of the ring
same
the prefix trans indicates that they are on … sides of the ring
opposite
the cis isomer cannot be converted to the trans isomer and vice versa without … and … one or more bonds
breaking; refomring
the cis isomer is approximately higher in energy than the trans isomer because of the … of the methyl groups on adjacent carbons in the cis isomer
steric strain
a stereocenter is an atom, most commonly carbon, about which …. produces a different
exchange of two groups; stereoisomer
configuration refers to the arrangement of atoms about a …
stereocenter
the most important property of alkanes and cycloalkanes is their almost complete lack of
polarity
alkanes are nonpolar compounds and only weak interactions exist between their molecules. … are the weakest intermolecular attractive forces
dispersion forces
the existence of dispersion forces accounts for the ability to … low-molecular weight, nonpolar substances
liquefy
dispersion forces: at any instant, there is a nonzero probability that electron density will be … (shifted) more toward one part of the atom than toward another . this temporary polarization creates a temporary …, which in turn induces temporary dipole moments in …
polarized; dipole moment; adjacent atoms
the small attraction referred to as dispersion forces is the source of … between temporary dipoles. the strength of dispersion forces depends on how easily an electron cloud can be …
electrostatic attraction; polarized
electrons in smaller atoms and molecules are held closer to their nuclei, and, therefore, are not easily … The strength of dispersion forces tends to increase with increasing … and …
polarized; molecular mass; size
the boiling points of alkanes are … than those of almost any other type of compound of the same molecular weight
lower
both boiling and melting points of alkanes … as molecular weight increases, but the increase in melting points is not as regular as that observed for boiling points
increase
alkanes containing 1 to 4 carbons are… at room temperature; those containing 5 to 17 carbons are … high molecular weight alkanes are …, …
gases; colorless liquids; white, waxy solids
all liquid and solid alkanes are … dense than water
less
alkanes that are constitutional isomers are … compounds and have … physical and chemical properties
different; different
the more branching there is the … the boiling point. as branching increases, the shape of an alkane molecule becomes more … and its surface area …
lower; compact; decreases
as surface area decreases, contact among adjacent molecules decreases, the strength of … decreases, and … decrease. thus, for any group of alkane constitutional isomers, the least branched isomer usually has the … boiling point and the most branched isomer usually has the … boiling point
dispersion forces; boiling points; highest; lowest
alkanes and cycloalkanes are quite … toward most reagents
unreactive
the … of alkanes by o2 to give … and … is by far their most economically important reaction. they act as energy sources for heat. the energy of the products is less than that of the reactants, with the difference in energy being given off as the …
oxidation; CO2; water; heat of combustion
as branching increases, the … decreases. therefore, we conclude that branching .. the stability of an alkane
change in enthalpy; increases
strain energy is the difference between the predicted and actual
heats of combustion
natural gas consists of 90-95% methane with lesser amounts of … and other low weight hydrocarbons
ethane
petroleum is a liquid mixture of literally … of different hydrocarbons. the most important processes in petroleum refining are …, …, and …
thousands; fractional distillation; catalytic cracking; catalytic reforming
synthesis gas: a mixture of … and …, can be derived from natural gas or coal
carbon monoxide; H
