The document discusses computational studies of the bond dissociation energy (BDE) of hindered amine (HALS) stabilizers. Four theories (B3LYP, HF, AM1, MP2) were used to calculate the BDE of two HALS molecules with protonated and non-protonated nitrogen. The B3LYP theory provided results closest to experimental data. Substituting aromatic rings with OCH3 or NO2 groups did not significantly affect BDE. Protonated nitrogen forms had higher BDE, indicating greater stability, than non-protonated forms. Larger substituent groups on HALS molecules decreased BDE, with stability increasing from H to CH3 to C(CH

1. Hindered amine stabilizes
By
Awad Nasser Albalwi
(June,2010)
1

2. CONTENTS
 Abstract
 Introduction
 The project proposal
 Procedure
 Results
 Discussion
 Conclusion
2

3. Abstract
 A B3LYP, HF, AM1 and PM2 computational studies of the reaction of
hindered amine (HALS) has been perfumed. Four different theories were
used to calculate the bond dissociation energy (BDE). In two molecules
studied the nitrogen were protonated and not protonated. BDE were
calculated when aromatic rings were substituted with NO2 and OCH3.
B3LYP was the best theoretical calculation level, The BDE was grater
when nitrogen in HALS was protonated. There was no big significant
difference in BDE when aromatic ring of hindered amine was substituted
with NO2 and OCH3.
3

4. Introduction
 Hindered amine light stabilizers (HALS) are among the most efficient polymer stabilizers
known. Bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate, is a typical (HALS).
 Since the early 1970s, HALS have become a highly important class of light stabilisers for
polymers. They stabilise wide range of commercial polymers and are particularly
effective for stabilization of polyolefins when use where resistance to deterioration by
light and weathering are important.
 Hinder amines have also been used as stabiliser against light induced degradation of
polymers such as polyolefin and polyurethane1&4
.
 Polypropylene is an example of a major commercial polymer which would never have
achieved any practical use without the development of a good stabiliser system.
 Polyolefin needs protection in all the stages of its life cycle. In order for an antioxidant
to improve the long-term weathering performance of an automotive clearcoat/basecoat
paint which is a polymer system, it must inhibit clearcoat photo-oxidation at the onset of
exposure and sustain the inhibition for many years.
 While there is sample evidence that hindered amine light stabilizer (HALS) additives can
inhibit the photo-oxidation of automotive clearcoats polymer,
4

5. Introduction
 Polyolefin needs protection in all the stages of its life cycle. In order for an antioxidant
to improve the long-term weathering performance of an automotive clearcoat/basecoat
paint which is a polymer system, it must inhibit clearcoat photo-oxidation at the onset
of exposure and sustain the inhibition for many years.
 While there is ample evidence that hindered amine light stabilizer (HALS) additives can
inhibit the photo-oxidation of automotive clearcoats polymer,
 HALS acts as a scavenger for free radicals that would otherwise degrade or discolour
HALS are efficient inhibitors of the photooxidation of polyolifins HALS act as
scavengers for free radicals that would otherwise degrade or discolour the polymer
coating.
 Hindered amine has been employed in the automotive and wood coating sectors of the
surface coatings industry for many years.
5

6. The purpose of this paper
 The purpose of this paper to examine the following hypothesis:
 There is correlation / relationship between an increase the size of group (R)
and an increase the Bond dissociation energy of Hindered amine (HALS).
 There is no effect of substitution on the aromatic ring of HALS with OCH3&NO2
in various positions.
 There are differences in BDE between none & protanated nitrogen of Hindered
amine (MO1).
 There is no relationship between change of such group (OCH3, NO2) on the
same position on the aromatic ring (HALS) & BDE changes.
6

7. In this project the molecular MO1 and MO2 is refer to this structure:
R R
MO1
Non-protonated
MO1(+)
protonated
R R
MO2(+)
Protonated
MO2
Non-protonated
7

8. Procedure
 Firstly, the calculations were performed with the GAUSSIAN09 (G09)
programme in order to select the best level of theory to calculate the Bond
Dissociation energy (BDE). Four level of theories (B3LYP, AM1, HF & MP2)
at the basis set 3-21(G) were used to calculate the BDE of these reactions
(Scheme3&4):
 Scheme3: breaking reaction of the bond O-R of Hindered amine MO1 .
8

9. Procedure
Scheme4: breaking reaction of the bond O-R of Hindered amine MO1(+)
9

10. Procedure
 In order to calculate the BDE, the reactants and products structures were built by drawing
each of them on the built molecule page in the job manager (GAUSSIAN09 (G09)).
 After constructing the molecule, comprehensive cleanup using idealized Geometry &
Mechanics was used to get the best molecular structures. .
 In addition the theory level was basis set, optimize + Vibe freq calculation, charge and
multiplicity were selected from Configure Gaussian Job Options page.
 After the calculation was done successfully, the electronic energy for every molecule was
determined from the final block of output of (G09).
 The BDE was calculated by using the formula:

 BDE = ∑ reactants energy -∑ products energy
 Comparison between the 4 levels of theories was done.
 Comparison of the four level of theories depends on how long every theory takes and how
accurate they are.by using results from research papers and experimental data
 After selecting the suitable theory, the comparison between different basis sets of the
selected theory, in calculation time and BDE results were done.
10

11. Procedure
 By using the B3LYP 3-21G data sets (Optimize + Vib Freq - Gaussian )., BDE
of breaking reaction of the bond O-R, when the substituting the aromatic ring
with different groups such as OCH3 & NO2 in various position (meta, Ortho &
Para) were calculated. The calculation was applied when the nitrogen is
protonated & non protonated (scheme 5&6).
Scheme 5: Substituting the aromatic ring with group NO2 in various
position (meta, Ortho & Para).
11

12. Procedure
Scheme 6: Substituting the aromatic ring with group OCH3 in various position (meta, Ortho
& Para).
The results of this project were compared with experimental data and
different level theories from other research papers.
12

13. Results:
 Table.1 Comparison between experimental and calculated BDE (O_R) for HALS Molecular 1 (MO1)
]kJmol_
1[ BDE 3LYP BDE AM1 BDE HF BDE MP2 BDE exp
)from research
BDEPM3
paper(
BDEDFT
M1-OH= M1-O.+H. 271.65 162.34 199.10 185.15 291 296 279
M1-OCH3= M1-O. + CH3 140.46 120.76 111.62 96.04 197 178 185
MO1-OC(CH3)3 = MO1-O.
+.C(CH3)3
186.53 172.98 100.71 74.72 n/a 94 n/a
Graph.1.: Comparison between experimental and calculated BDE (O-R) for HALS
Moleculer1.
13

14. Results
Graph.2: Comparison of BDE when an increase of R from H to CH3 between
experimental, PM3, DFT from research paper & calculated with HF, B3LYP, MP2
and AM1.14

15. Results
Graph.3: The comparison of calculation time of energy with different levels of
theories
15

16. Results
Graph. 5: Comparison of BDE changes with an increase the basis sets of B3LYP
for HALS Molecular No.1 with different R group ( R=H, CH3 & C(CH3)3).
16

17. Results
Graph.6: Comparison of BDE between none & protanated nitrogen of Hindered
amine (MO1) with different group of R ( H, CH3 & C(CH3)3.
17

18. Results
Graph.7: Comparison between BDE change with HALS molecular No1 with different
group of R ( H, CH3, CH2CH3, CH(CH3)2 , C(CH3)3 ).
18

19. Results
KJ/mol
Graph.8: comparison between change the group (OCH3) on the aromatic ring of
HALS molecular No2 (MO2) – none protonated Nitrogen -and BDE changes at
B3LYP/3-21(G).
19

20. Results
Graph.9: comparison between change the group (OCH3) on the aromatic ring of
HALS molecular No.2 (MO2(+)) - protonated Nitrogen -and BDE changes at
B3LYP/3-21(G).
20

21. Results
Graph.10: comparison between change the group (NO2) on the aromatic ring of
HALS molecular No2 (MO2) – none protonated Nitrogen -and BDE changes at
B3LYP/3-21(G).
21

22. Results
Graph.11: comparison between change the group (NO2) on the aromatic ring of
HALS molecular No2 (MO2) – proton ted Nitrogen -and BDE changes at B3LYP/3-
21(G).22

23. Results
Graph.12: comparison of BDE between different groups (NO2 & OCH3) on the
aromatic ring of HALS molecular No2 (MO2) – none- protonated Nitrogen -at
B3LYP/3-21(G).
23

24. Discussion
 It is observed that very few experimental BDEs of HALS have been reported in literature.
 BDE of O-R in HALS compound have been investigated for various group ( R= H, CH3 & C
(CH3)3 using different level of theories and different data sets, Calculated BDE from research
papers were compared with calculated BDE in this paper (Table .1 and figure. 1) .
 It was found that the BDEs of O-R (HALS) were decreasing from H> CH3> C (CH3)3 using HF
& MP2 theories. However , the BDE was random from H> C(CH3)3 > CH3 using B3LYP &
AM.
 It was found that in most cases B3LYP/3-21(G) calculations were slightly closer to BDE
experimental value when R= H& CH3 .It is also observed that the results coming from HF &
MP2 were more reasonable, thus the stability of these groups were increasing from C (CH3)3 >
CH3>H. The stability of those group lead to decrease the BDE of O-R in HALS.
 It is interesting to note that the calculated BDE using B3LYP /3-21(G) of this paper was in
agreement with the experimental values . Graph.2 has shown that The B3LYP /3-21(G)
was closer R2
=0.86 to the experimental value & DFT (R2
= 0.99) level theory from journal
article than other theoretical calculation (HF, AM1 & MP2) 6
. Thus , It has chosen the
B3lYP/3-21(G) to calculate the BDE for various structures in this project . In addition, The
B3LYP/3-21(G) takes short calculation time Graph 3&4.
24

25. Discussion
 Figures 8 and 9 show the effect of substituting the aromatic ring with OCH3 in Meta, .or tho
and Para positions, there was no significant change in BDE when OCH3 was substituted on
all three positions of the aromatic ring.
 Figures 8 and 9 have shown that there was difference in BDE when the nitrogen is proton
ted and not protonted.
 In protonated Nitrogen the BDE is greater than that of non protonated by about 7% .
 figures 10and 11 show the substitution of NO2 on the aromatic ring, In figure .10 there was
no change in the BDE when NO2 was substituted in ortho and para positions. However
BDE decreased significantly in meta position and this is not normal compare to other
positions.
 Figure 12 shows comparison between 2 different substitutions ie NO2 and OCH3.on
aromatic rings. There were no different in BDE in ortho and para positions when NO2 and
OCH3 were substituted on the aromatic rings.
 However the BDE of OCH3 was three times greater than that of NO2 in meta position
figure.12.
25

26. Discussion
 Figure. 6 has indicated that protonated Nitrogen of HALS gives an increase in BDE than
non protonated . Thus the HALS (MO1) with protonated Nitrogen might be more stable
than non protonated Nitrogen
 In addition , protonated Nitrogen of HALS might lead to increase the lifetime of the paint
that contains the HALS Molecule.
 From the result , it can be said , the increase the size back rings of HALS is not significant
in an increase the stability of HALS in comparison between non protonated nitrogen of
MO1 & MO2.
 How ever, in protonated Nitrogen of MO1(+) &MO2(+) cases , the MO1(+) was greater in
BDE than MO2(+) (graph 6,9&11). Thus , the MO1(+) is more stable than MO2(+).
26

27. Conclusion
 Computational analysis now show that there is a relationship
between the size of R and BDE of HALS. cause When R
increases, BDE decreases. It is also observed that there was no
significant change in BDE when OCH3 was substituted on all the
three positions of the aromatic rings of HALS. Computational
calculations also show that there was difference in BDE between
protonated and non protonated nitrogen of HALS.
27

28. References:
 1-Possi, Aventurini and A Zedda J. AM Chem .SCI (1999)121,,7914-7917
 2-F,.Gugumus Polymer Degradation and Stability (1995) 50, 101-116
 3- P.P. Klemchuk , M.E Gande Polymer Degradation and Stability (1988),22,241-274
 4- T.A. Lowe, M.R.L Paine,D.L.Marshall.L.A.Hick,J.A.Boge,P.J.Barker , S.J.Blanksby J
Mass Spec (2010) 45(5) 486-496

 5- G.Geuskens ,M.N.Kanda Polymer Degradation and Stability (1996),51, 227-232.
 6- A Gaudel,S., D. Siri, P.Tordo ,ChemPhysChem,(2006),7,430-438
********************************
 Paine, M. R. L., Barker, P. J. and Blanksby, S. J. "Desorption Electrospray Ionisation
Mass Spectrometry Reveals In Situ Modification of a Hindered Amine Light Stabiliser
Resulting From Direct N-OR bond cleavage" Analyst 2011, 136 (5), 904-912. [Cover
Article]
28