1+2 book

Question 1

what is IR spectra a result of

Answer 1

a result of radiation exciting vibrational modes in a molecule

Question 2

what does the number of IR signals depend on

Answer 2

depends on the number of vibrational modes for a molecule

Question 3

total degrees of freedom

Answer 3

3N

where N is the total amount of atoms in a molecule

Question 4

amount of vibrational modes for a non linear molecule

Answer 4

3N - 6

3 trans and 3 rot

Question 5

amount of vibrational modes for a linear molecule

Answer 5

3N - 5

3 trans and 2 rot

Question 6

will all vibrational modes be seen as IR signals

Answer 6

nope!!!

Question 7

what happens to the amount of IR vibrational modes as the degree of symmetry increases

Answer 7

more symmetry = less vibrational modes in spec

Question 8

what is used to predict the number of absorption lines in spectra

Answer 8

group theory is used to predict the amount of absorption bands in the spectra

Question 9

give 2 examples of a symmetry element

Answer 9

planes and lines

Question 10

what is a group point symmetry

Answer 10

where all the lines of symmetry meet

Question 11

if smt undergoes a symmetry operation and ends up looking the same,, what does it mean about the 2 atoms

Answer 11

they’re in the same chemical environment

Question 12

label for a rotational element + operation

Answer 12

C

Question 13

element is theeee

Answer 13

line or plane

Question 14

operation issss

Answer 14

what is done to the molecule

Question 15

what label do we need for a rotating element or an operation

Answer 15

C

Question 16

subscript is theee

Answer 16

bottom number
tells us how many rotations are possible for the molecule to still look identical

Question 17

subscript can also be called

Answer 17

the order of rotation axisssss

Question 18

the superscript issss

Answer 18

the amount of the total rotations that was done to get a certain arrangement

Question 19

what’s one way to think of superscripts and subscripts when looking at a rotation operation label

Answer 19

think of it like 2/3

so we rotated it 2 of the total 3 ways we could

Question 20

what is the principal axis

Answer 20

this is the line of symmetry with the largest order // subscript value

Question 21

between C5 and C2 which would be the principe axis

Answer 21

C5
it’s the largest order
making it the best principle axis

Question 22

what do we do about the principal axis

Answer 22

we set this as the vertical axis
we say it’s aligned with the z axis

Question 23

do symmetry elements move when operations occur

Answer 23

nope!!
the lines and planes stay in the same place,, only the molecule moves

Question 24

C6 can be split intoooo

Answer 24

C1 6
C5 6
C2 3
C1 3
C2

Question 25

if both elements are called C2 how can we tell them apart

Answer 25

use
C2’ if it’s going through an atom
C2’’ if it’s going through a bond

Question 26

arbitrary principal axis

Answer 26

when u choose which axis will be the principal one

u just need to make sure u make it known using cartesian axis
C2 (y or x or z)

Question 27

what is the plane of symmetry symbol and when is it seen

Answer 27

it’s a sigma sign

it’s seen when a reflection gives the same orientation

Question 28

when the plane of symmetry is in the plane of the molecule,, how do we write it

Answer 28

sigma ‘

Question 29

when the plane is not in the plane of the molecule, how do we write it

Answer 29

just the sigmaaaa

Question 30

if there’s only one axis,, what will be the principal one

Answer 30

that one!!
that one would align with the z axis and be set as vertical

Question 31

how do we tell if a plane is vertical or horizontal

Answer 31

sigma v ‘
sigma v

Question 32

remember that z is set to the principal axis,, which is the axis withhhh

Answer 32

the highest order axis

Question 33

plane of symmetry with the principal axis in it issss

Answer 33

vertical
sigma v

Question 34

when do u add ‘

Answer 34

if the line goes through an atom
if the symmetry plane is in plane with the molecules plane

it would be going through z and y

Question 35

which axis is perpendicular to z

Answer 35

x axisssss

Question 36

how to say plane in the zy axis in the plane of the molecule

Answer 36

sigma for the plane of symmetry
v for it being vertical
‘ for it matching the plane
(zy)

Question 37

plane of symmetry which has the principal axis within it issss

Answer 37

sigma v

bc principal is the new vertical

Question 38

plane of symmetry that matches the plane of the molecule

Answer 38

sigma h

bc it’s not vertical bc it doesn’t have the principal axis which would make that plane vertical

Question 39

plane of symmetry that matches the plane of the molecule

Answer 39

sigma h

bc it’s not vertical bc it doesn’t have the principal axis which would make that plane vertical