They were principally used to catalyze aldol, allylation, Diels - Alder, ene and Friedel - Crafts reactions.是什么意思？

They were principally used to catalyze aldol, allylation, Diels - Alder, ene and Friedel - Crafts reactions.

它们主要被用来催化Aldol, 烯丙基化, Diels-Alder, Ene和 Friedel -Crafts等反应.

they

pron. 他/她/它们，人们，大家，政府，当局，她们；

例句
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。

were

be的过去时复数和第二人称单数形式，有时代替 was,用于条件从句、动词 wish 之后等；

例句
Shops, houses, and vehicles were set ablaze.
店铺、房子和车辆全都陷于火海。

principally

adv. 主要地，大部分；

例句
This is principally because the major export markets are slowing...
这主要是因为主要出口市场发展缓慢。

used

adj. 用过的，习惯于，二手的，旧的；v. 使用（ use的过去式和过去分词），常常，经常；

例句
The gym can be used by both able-bodied and disabled people.
这家健身房健全和残障人士都可使用。

to

prep. 向，朝着，到，关于，属于；adv. 朝一个方向的，到某种状态，关闭；

例句
I suggest you leave it to an expert...
我建议你把它留给专家来解决。

catalyze

vt. 催化，促进；

例句
Any unexpected circumstance that arises may catalyze a sudden escalation of violence.
任何突如其来的情况都可能造成暴力骤然升级。

aldol

n. 丁间醇醛；

allylation

烯丙基化（作用）；

alder

n. 桤木；

例句
Modification for synthetic purposes on the Diels - Alder adducts 56 and 62 has only rarely been considered.
为了达到合成的目的,对Diels-Alder加 成物(56)和(62)加以改造的问题很少有人考虑.

and

conj. 和，与，而且，于是，然后，因此；

例句
I spend a lot on expensive jewelry and clothing...
我花很多钱购买昂贵的首饰和衣服。

Crafts

n. 工艺( craft的名词复数 )，行业，飞机，飞行器；

例句
...the arts and crafts of the North American Indians...
北美印第安人的手工艺

reactions

n. 反应( reaction的名词复数 )，反动，反对，反作用力；

例句
Soya milk can cause allergic reactions in some children.
有些孩子会对豆浆过敏。